The Llano, together with its southward extension, having the same characteristics and known as the Edwards plateau, is bordered on the west by the deep and broad valley of the southward-flowing Pecos River, and on the north by the equally deep and broad valley carved in the plateau country by the eastward-flowing Canadian River. The eastward slope of the surfaces of the two plateaus is continued throughout the region bordering them on the east all the way to the shore of the Gulf of Mexico. The streams originating on the eastern border of the eastward sloping plateaus and flowing to the Gulf of Mexico, represented at the present time by the Colorado (of Texas), the Brazos, Trinity, and Red Rivers, extended their trunks by head-water corrasion and developed numerous branches so long as the rainfall was sufficient to maintain a surface drainage. But as the streams were lengthened they cut farther and farther westward and into a region that became drier and drier, until finally they reached a land in which all of the scanty rain that fell was absorbed by the thirsty soil. The drainage from this higher and drier region is subterranean, and reaches the head waters of the streams to the eastward to a considerable extent as springs. The streams which lowered the country to the eastward of the Llano developed many branches, some of which were extended westward into the drier plateau country in such a manner as to give the eastern margin of the remaining upland a scalloped and irregular border.

In travelling westward up the courses of the rivers of eastern Texas, one passes from a low region of old topography to one where the head branches of the streams flow in cañons, and the relief has the ruggedness of youth; on gaining the western border of the belt of country having surface streams one ascends to the smooth surface of the high plateau, which is young as regards stream development, although in years older than the country with a deeply eroded surface to the eastward. The Llano and Edwards plateau present us with examples of perpetuated topographic youthfulness.

The Llano, although dreaded by early explorers and shunned so far as possible even by experienced plainsmen, on account of a lack of water, has in recent years become more favourably known. It is crossed at present by two railroads. Water has been found beneath the surface in numerous localities, and the desert-like region now bids fair to become a favourable cattle-raising country. It is not to be expected, however, that all the glowing predictions which have been published concerning this and neighbouring table-lands will be more than partially fulfilled through the use of the subsurface waters.

The Arkansas Plateau.—To the north of the Canadian River the region termed above the Great plateaus is less deeply dissected than in the portion of which the Llano is typical, and the streams from the mountains flow through shallow valleys with less rugged and less picturesque borders than those of the deep wide valleys of western Texas and eastern New Mexico. The broad plateau surfaces adjacent to the valleys of the Arkansas and Platte Rivers probably come nearer to the popular idea of the essential characteristics of the "Great plains" than any other of the larger divisions of the region under review. The most conspicuous geographic features of the Arkansas plateau have been described by W. D. Johnson as consisting of an assemblage of low and broad table-lands separated by shallow erosion valleys. The plateaus are immense unsculptured remnants in light relief of an older and originally perfect plain. The few long and feeble streams, wide apart and flowing eastward from the distant mountains in parallel courses and without tributaries, have blocked out by dissection the larger features of the broad landscape which in future ages will be slowly etched into a multitude of details. The scenery of these featureless plains is ordinarily depressing when once the novelty of being adrift on a sea of grass has passed away. There is nothing that can be termed scenery except that which once a year for a brief period the sky affords when clouds of extraordinary grandeur darken the air. Throughout nearly the entire annual course there is no material for landscape effect except the straight line of the horizon with a featureless breadth of sun-faded brown below it and above a merely broader space of faded blue. There is nowhere a curved line, and though as a scientific fact there is vast expanse of flat plain, there is little to suggest it when the sky is empty of clouds. In June the clouds come with a gradual maturing at some point along the even sky-line, and increase rapidly until the heavens are filled with magnificent vapour banks; but the display is simply spectacular, and passes away in a few hours as quickly as it came, with only local showers to refresh the land.

The one industry that can thrive on the Arkansas plateau, which was formerly at certain seasons blackened by herds of bison, is stock-raising. Wells from which water is pumped by windmills furnish sufficient water for herds of cattle and horses, but not for irrigation.

Bad Lands.—In the northern portion of the Great plateaus within the United States the surface rocks over great areas are soft or but irregularly hardened sediments of ancient lakes and streams and have been sculptured by rain, wind, and ephemeral rills into a most marvellous array of monumental and castellated forms. Localities where this minute dissection of the soft horizontal strata is especially well marked over hundreds of square miles occur in South Dakota and Montana, and especially on the borders of the valleys carved by the Loup Fork, Niobrara, White, Yellowstone, and Missouri Rivers. In this region the rainfall is light, the mean annual precipitation being in the neighbourhood of 15 inches, and occurs mostly during the winter months. In the summer season the lands far out on the plateaus are dry and hot, and all but the larger streams disappear. The rocks, consisting mostly of unconsolidated clays and soft sandstones, with occasional hard layers and irregular concretions, have been cut into innumerable channels, leaving steep-sided remnants of the former plain between. The maze of trench-like valleys, the similarity of the sculptured land-forms one to another, and the absence of water, make these desert regions excessively difficult to traverse. The Canadian-French who explored the north-central portion of the Great plateaus in early days of American settlement termed these tracts of country, so difficult to cross, Mauvaises Terres, a name now seldom used, but replaced by the English name Bad Lands. Although bad to the hunter and the plainsman, these desert regions are of fascinating interest to men of scientific training. The intense heat, the choking alkaline dust, the absence of water, and the danger of being lost and of perishing of thirst in these wild silent regions, have not checked the ardour of explorers. Not only do the Bad Lands present a most attractive field to the student of erosion and of the origin of earth forms, but their deathlike solitudes have been made to yield the most wonderful procession of strange extinct animals yet unearthed by geologists. They are vast cemeteries in which are interred the skeletons of many genera and hundreds of species of animals which lived in the ancient lakes or wandered through the almost tropical forest that in distant ages clothed the adjacent country. The great lesson to be learned by the geographer in these uninviting regions as they seem to most people relates to the way in which the rocks have been eroded. The prevailing softness of the beds with occasional hard layers, the scarcity of vegetation, the occasional heavy rains, and the considerable height of the country above the master streams combine to favour rapid and deep sculpturing. The precipitous slopes of the small mesas and castle-like rock forms destitute of all vegetation excepting succulent cacti and scattered clumps of bunch-grass, reveal a multitude of sunken lines and raised edges, produced by the ephemeral streams, and a less complex series of horizontal ledges due to the prominent edges of hard layers. The steep slopes are worn into alcoves and irregular recesses by the transient rills, and smoothed or etched by the wind-driven sands. The result is an assemblage of architectural forms such as only the most fantastic dream pictures or the strange tricks of the mirage on northern ice-fields can simulate. Nor are the wonderfully intricate topographical forms the sole attraction. The rocks are variously coloured, and present endless combinations of yellow, red, green, purple, etc., in many tints and shades, rendered seemingly brilliant by contrast with the gray of shales and the blackness of occasional coal-seams. Owing to the burning of coal-beds, the rocks are sometimes altered over broad areas and given unusually striking colours, among which various shades of red predominate. Standing on some commanding crag in the Bad Lands in the early morning or when the purple shadows of evening fill the gorges and ravines, the most unimaginative traveller sees in the silence about him the ruins of a vast city, with cathedrals, temples, and palaces of varied colours and weird designs such as no mortal hand ever fashioned. It is at such times that the picturesque and gorgeous, although desolate, landscape kindles the fancy and suggests day dreams which distract one's attention from the more prosaic study of these earth ruins.

The best developed portions of the strange region here referred to occur on the borders of the uplands overlooking the larger valleys, excavated by the rivers flowing eastward from the mountains, and are simply larger examples of erosion, such as may be seen in many bluffs and valley-sides in nearly every country, but rendered conspicuous by their size, extent, endless variety, and unusual colours.

Sand-Hills.—The sands winnowed by the winds from the bare plains and steep bluffs are in certain places on the Great plateaus gathered into dunes which cover great areas with a succession of low dome-shaped hills. On the borders of the Niobrara River there is a detached area of about 20,000 square miles, which has been covered in this manner with loose sands. This region, as described by F. V. Hayden, presents a succession of round-topped hills, some of them scooped out by the swirling winds so as to resemble volcanic craters. These sand-hills were formerly a favourite resort of the bison, which fed upon the scanty but very nutritious grasses in the little valleys and intervals among the mounds and ridges. There is, for the most part, an abundant supply of water in the lakelets scattered through the region, and fed by the seepage from the porous sands, which drink in all the water that falls upon them and allow it to percolate slowly into the adjacent depressions. Some of the lakelets and ponds are highly alkaline, while others are fresh; the former can be easily distinguished from the latter by the absence of vegetation about their borders. The hills, although seemingly utterly desolate, on a nearer view sometimes reveal considerable vegetation, including yuccas or "Spanish needles," which shelter the sands from the winds.

Many other regions on the western border of the Great plateaus, in the valleys of the Rocky Mountains and on the desert plains of Utah, Nevada, and California, are buried beneath drifting sands, which have the characteristic features of a dune-covered seacoast. The sources of the sands in these interior plains are usually to be found in the disintegration of the rocks under the action of the dry air with its many and sudden changes of temperature, but occasionally they come from desiccated lake beds not yet clothed with vegetation.

Central Portion of the Great Plateaus.—The State of Nebraska, about 400 miles in length from east to west, and extending across the Great plateaus to within some 60 miles of the mountains bordering them on the west, furnishes a typical example of the west-central portion of the interior Continental basin. As described by Hayden, this State may be divided into two portions, one agricultural and the other pastoral. The eastern part, included in the Prairie plains, contains some of the most beautiful, gently rolling, and fertile agricultural lands in America. But the western part is a treeless, almost waterless plain; yet thick, low, sweet, nutritious grasses cover the entire surface, and render it well adapted for the raising of large numbers of horses, cattle, and sheep. Over western Nebraska not more than 15 or 20 inches of moisture fall annually; the snows of winter are very light and soon pass away, the winds rapidly gathering them into the valleys and gorges, leaving vast areas entirely bare. The grasses, instead of decaying, as in all temperate countries with a humid climate, slowly wither, retaining all their nutritious qualities, and thus continue until April or May, when the fresh shoots spring up, so that all kinds of stock thrive throughout the winter on the open plains without artificial shelter. In this account, however, the author cited fails to note that the winters are frequently marked by exceedingly severe storms termed blizzards, during which gales blow while the temperature is far below freezing, and that at such times cattle have been known to perish by thousands.

In late summer and autumn the streams in this portion of the plateau region for the most part become dry, although water may usually be discovered at long intervals in pools in their beds. In ascending the valleys the water appears and disappears as if by magic. Here one finds a swift-running stream several yards broad, and then for a considerable distance nothing is to be seen but a dry and dusty creek bed, resembling a sunken roadway. Even the broad Platte has so far forgotten itself for several seasons as to cease to be a running stream. It is not uncommon for a river originating in the mountains on the west to be considerably larger towards its source than near its mouth. Many of the important streams that flow from the Black Hills towards the Missouri are lost on their way through the plains. The Yellowstone and the Missouri, the two most important rivers crossing the Great plateaus in the northern portion of the United States, retain their existence throughout the year, although becoming greatly shrunken in autumn, and send eastward a never-ceasing tribute to the Mississippi.

Northern Extension of the Great Plateaus.—The Great plateaus cross the United States-Canadian boundary and extend northwestward through the western portion of Assiniboia and Saskatchewan, and embrace nearly the whole of Alberta and western Athabasca. At the international boundary the plateau region is about 470 miles broad, and extends from longitude 103° 30' westward to the foot-hills of the Rocky Mountains, and in this region embraces what is frequently termed the third prairie steppe, known in part as the Missouri Coteau. The east border of this high plateau throughout much of its extent is well marked by an escarpment which descends some 300 or 400 feet to the second prairie steppe, which together with the first or most easterly of the series, embracing the Red River Valley, is usually considered as belonging to the Prairie plains. The third steppe in the series, or the one extending from the Red River to the Rocky Mountains, has an elevation along its eastern border of about 2,000 feet, rises gradually to the westward, and attains a general elevation of over 4,000 feet on its western border. All of the region of the Great plateaus north of the international boundary, with the exception of about 20,000 square miles tributary to the Missouri, is drained by rivers flowing eastward to Hudson Bay or northward to the Arctic Ocean. It is thus a portion of the northern or arctic slope of the Continental basin. The eastern border of the plateau country trends northwestward, and finally reaches the Rocky Mountains in the vicinity of the head waters of the Mackenzie, but as this region is but imperfectly explored, our knowledge of the boundaries of the natural division of the continent we have been endeavouring to trace there becomes indefinite. The Great plateaus in Canada merge into the Prairie plains bordering them on the east, and in large part the position of the dividing line between the two is arbitrary.

The portion of the Great plateaus in Canada, like the similar region to the south, is covered with bunch-grass, which dries as it stands and forms highly nutritious self-cured hay. Formerly this region was the winter feeding-ground for vast herds of bison. The winters, although cold, are not characterized by a heavy snowfall, and even in midwinter the warm dry chinook winds, as they are termed, similar to the foehn winds of Switzerland, frequently cause the snow to disappear and leave the brown plateau surfaces free for grazing. Now that the bison has disappeared, this immense region is favourable in many ways for stock-raising, but, unlike the lower prairies to the east with their rich black soil and long hot summers, is not suitable for agriculture. The main difficulties in the way of successful farming lie in the dryness of the summers, and the scarcity of water available for irrigation. The rivers flow in valleys several hundred feet below the general plateau surfaces, and hence cannot be made available for irrigating the uplands without too great an expense. In the bottoms of the valleys, however, adjacent to the stream, limited areas are now under cultivation, and it is to be expected that the wheat-fields of the prairie region will be gradually extended into the valley to the westward, and perhaps even to the eastern margin of the plateaus. A greater extension of the wheat-belt to the north and west than is now thought practicable has been predicted, but what the ultimate limit will be cannot be told.

The Black Hills of Dakota.—As stated in the brief account already given of the Prairie plains, their monotony of surface and of geological structure is broken by a single area of disturbance termed the Ozark uplift. Similarly, the vast generally level expanse of the Great plateaus is broken by a single rudely circular region of elevation, the Black Hills of Dakota, which has been sculptured by atmospheric agencies and given a diversified topography, in striking contrast with the even monotony of the country surrounding it.

This protuberance on the surface of the Great plateaus is situated in the southwest portion of South Dakota, and embraces also a part of Wyoming, and about 140 miles east of the nearest range—the Big Horn Mountains—of the Rocky Mountain chain. It rises from the surrounding plateau to a height on an average of about 2,000 to 2,500 feet; the highest summit, Harney Peak, is 3,000 feet above the plain, and 7,216 feet above the sea. The uplift is elliptical in ground plan, with a northwest and southeast axis measuring about 120 miles, and a transverse diameter of 40 to 50 miles. Its area is in the neighbourhood of 6,000 square miles.

While the generally level plateau surface about the Black Hills is treeless, except for the scattered groves of wide-spreading cottonwoods along the immediate banks of the larger streams, the central and higher portions of the elevation itself is clothed with an open but abundant forest, consisting principally of pines. The evergreen forests give to the hills a nearly black colour when seen from a distance, and have gained for them the name they bear.

The rocks which have been forced upward so as to form the Black Hills dome were previously like those in the surrounding plain, quite horizontal, and had a vertical thickness of at least 5,000 feet. The uplift, if uneroded, would rise from the surrounding plain as a flat-topped dome about 6,600 feet high, as is suggested by the highest dotted line in the following diagram. In reality such a dome never existed, for the reason that its growth was slow, and perhaps is not completed even at the present day, and as soon as the rocks began to rise, the rain, wind, streams, etc., commenced their task of destruction. The higher the rocks were elevated the more powerfully those agencies acted. The top of the dome was soon broken and its internal structure revealed.

By reference to the accompanying generalized section through the Black Hills, which as the uplift is rudely circular would be essentially the same if taken in any direction through the elevated region, it will be seen that there is a central core of slate, schists, and granite which has been forced upward so as to stand in its present eroded condition; it rises well above the surface of the adjacent plateau. About this central core the upturned edges of the sedimentary rocks form concentric zones, the oldest in the series being next the schists, and the youngest 10 to 40 or 50 miles distant. It is the presence in the central part of the hills of an area of resistant crystalline rocks which have weathered into rugged forms, and the series of encircling and concentric belts of rock of varying degrees of hardness and solubility, that has given to the uplift its present peculiar relief and its generally beautiful scenery. The edges of the harder belts form bold hills and ridges, while the softer belts have been eroded into valleys. This series of sharp-crested ridges and intervening valleys forms concentric circles completely surrounding the central group of rugged mountains. The largest and most interesting of the ring-like valleys is underlaid by red sandstone, and is remarkable for its flaming colour as well as for its exceptional form. In this Red Valley one may ride entirely around the rugged central mass of the hills, on a generally level surface, which is inclosed on its outer border by a precipitous wall of yellowish sandstone and shale 300 or 400 feet high. The distance about this "race-course," as it is sometimes termed, is about 200 miles. This series of concentric ridges and intervening valleys, surrounding a high and rugged region of more resistant rock, furnish an admirable illustration of the influence of rock texture, hardness, etc., on topography.

Another instructive geographical lesson afforded by the Black Hills is the manner in which the portion of the dome rising above the level of the rivers which flow across the surrounding plain has been dissected by stream erosion. The streams originating in the central portion of the uplift flowed outward in all directions, and have cut deep narrow gorges through the ridges of hard rock in the base of the truncated dome. Some 20 streams originating in the central portion of the uplift cross Red Valley and escape through notches in its outer wall, about 16 of which are well-defined gateways leading to the encircling plateau. This is one of the most beautiful and most instructive examples of consequent drainage—that is, of streams whose direction has been determined by the inclination of the surface over which they flow—thus far discovered. Still another feature of much geographical interest is furnished by the rivers on the adjacent plain, two of which, branches of the Cheyenne River, cross the north and south extensions, respectively, of the Black Hills dome. These streams flow directly across the arched strata, in cañons of their own making, and, as explained by G. K. Gilbert, are illustrations of superimposed drainage—that is, the portions of the dome crossed by the branches of the Cheyenne after the rocks were upheaved were covered by soft horizontal lake beds, over which the water flowed as consequent streams. The rivers deepened their channels and cut through the soft cover of horizontal rock and into the arched beds beneath. The course of the streams initiated on the covering of soft beds were maintained, as the flowing water charged with sand cut downward into the harder, upturned beds beneath, and now, the covering of soft beds having been eroded away, the rivers flow directly across (or through) the flanks of the great arch, but are not deflected by it.

In the neighbourhood of the Black Hills, and especially about their northern and northwestern border, there are secondary hills formed by the upward protrusion of molten rocks into the generally horizontally stratified rocks underlying the plateau. These intrusions did not reach the surface in such a way as to form volcanoes, but were forced upward, raising domes above them, in which the structure is similar to that in the great Black Hills dome. These secondary domes have been eaten away by erosive agencies in varying degrees. In some of them, as the Little Sundance Hill, near the town of Sundance, Wyoming, the dome of stratified rock is unbroken, and no igneous rock is to be seen; other neighbouring domes in which the plutonic magmas rose higher have been eroded so as to expose the summit portion of the inner core; and in one instance, known as Mato Tepee, the uncovering of the plug of plutonic rock which caused the uplift is so complete that it now forms a prominent fluted column over 600 feet high above its immediate base.

Volcanic Mountains and Table-Lands.—In the south-central portion of the Great plateaus in southwestern Colorado and eastern New Mexico, there are several typical cinder cones with lava-flows associated with them, which impart novel topographic forms to the general monotony of the broad plateau surfaces. The highest of the extinct volcanoes in this region is Mount Capulin, situated in northeastern New Mexico, about 200 miles east of the Rocky Mountains, which rises 2,750 feet above the surrounding plain, and has an elevation of about 9,000 feet above the sea. At the summit of this conical mass there is a well-defined crater a mile in diameter. In the same region there are several other similar volcanic cones, from which lava streams have descended. As has been pointed out by R. T. Hill, these are the most easterly volcanoes of recent geological age in North America. They were formed after the Tertiary rocks of the Llano were laid down.

The Raton Mesa, situated between Mount Capulin and the front range of the Rockies, is capped by a lava flow of more ancient date than the volcanoes just referred to, which has protected the softer rocks beneath from erosion, and now stands as a prominent table-land with precipitous borders.

To the west of the Continental basin is a vast cordillera composed of numerous mountain chains which extends from south-central Mexico northward to the Arctic Ocean, and in its broadest part is about 1,000 miles wide. As already explained, we speak of this region in its entirety as the Pacific cordillera, or less technically as the Pacific mountains. It is a highly complex group of mountain chains, each of which contains two or more distinct mountain systems; each system, again, is usually composed of many ranges, and each range is frequently made up of a multitude of ridges, peaks, buttes, mesas, etc.; there are also many plateaus more or less completely dissected by erosion, and broad valleys, as well as numerous cañons, gulches, ravines, arroyas, and other secondary topographic forms. This vast cordillera not only contains mountains produced by the folding of the rocks of the earth's crust, in a general way similar to the Appalachians in structure, but also upturned blocks many miles in extent, bounded by breaks or faults, and volcanic mountains, vast lava-flows, and elevations due to the injection of molten rock into the earth's crusts so as to elevate domes. In fact, scarcely any topographic form and no important geological structure that is known is lacking in this great family of mountains which dominates the western portion of the continent.

The Pacific mountains begin abruptly at the south, along a generally east and west line passing some 75 miles south of the City of Mexico, where the precipitous border of the table-land of central Mexico overlooks a lower region to the south which is diversified by many volcanic mountains. But little accurate information is available concerning the geology and geography of Mexico, but in general, as is well known, there are three main mountain belts which traverse that republic. One of these mountain belts is adjacent to the Gulf of Mexico, and another is situated near the Pacific coast of the main portion of the republic, while the third forms the rugged and irregular axis of the peninsula of Lower California. Between the leading mountain belts of the mainland there are numerous short ranges and many nearly level-floored valleys. The general level of this inland region is in the neighbourhood of 6,000 feet, while the more prominent peaks and crests attain elevations of from 10,000 to 12,000 feet. The general trend of the main mountain belts, and of the numerous subordinate ranges, is about northwest and southeast. For this reason, and also because the valleys have become deeply filled with débris from the mountains, travelling in directions leading north and south is facilitated by the topography, while in passing from one coast of the republic to the other the rugged bordering mountain belts have to be crossed and detours made in order to pass around the central mountain ranges.

The more elevated portion of central and northern Mexico, together with the peninsula of Lower California, has an arid climate, to which many of the conspicuous features in the geography of the land are due. The precipitation over large areas is insufficient to maintain permanent streams, the vegetation is nearly all of a desert-like character, and several basins exist which do not drain to the sea. In the interior basins there are saline and alkaline lakes, and numerous dry lake beds or playas, which are whitened by saline efflorescences. The rocks exposed in the mountains are largely of sedimentary origin, but a characteristic feature is the geology, especially to the west, in the presence of extensive volcanic areas and lofty mountains of igneous rocks.

The Pacific cordillera begins in southern Mexico with a width of some 300 miles and broadens when traced northward. At the boundary between Mexico and the United States it has a width of fully 700 miles, but reaches its greatest breadth in the latitude of San Francisco and Denver, where it is about 1,000 miles across. In its better known, but as yet incompletely studied portion embraced within the boundaries of the United States there are several important subdivisions, such as the Rocky Mountain belt on the east; a less lofty, but yet rugged central region, termed the Great Basin, characterized by having a dry climate and by the fact that the streams do not reach the ocean; and a western mountain chain which includes the Sierra Nevada and Cascade Ranges. To the west of the mountains just named lies the great valley of California, and similar regions in Oregon and Washington occupied in part by Puget Sound. To the west, again, are the several ranges bordering the Pacific coast from Lower California to Vancouver Island, and termed in a general way the coast mountains. Each of the great divisions of the Pacific mountain region has its indefinitely known southern terminus in Mexico, and extends northward to beyond the Canadian boundary. As this central portion of the most westerly of the larger geographical divisions of the continent is well developed in the United States, and has there been more carefully explored than elsewhere, a review of its leading features will serve to give as good an idea of the entire Pacific mountain region as is now practicable.

The Rocky Mountains.—The limitations to the north and south of the region to which this name is more or less specifically applied are not well defined. Perhaps the most accurate statement at present permissible is that the Rocky Mountains begin at the south, in northern Mexico, and extend northward across the United States and Canada to near the shore of the Arctic Ocean. On the east it is sharply defined by its junction with the Great plateaus. Its western border, although less definite than the eastern, is easily traced, at least across the greater portion of the United States, by the marked contrast it presents to the geographical conditions characteristic of the Great Basin region, but owing to the many difficulties met with in attempting to adjust and make use of the current nomenclature in classifying geographical regions more or less artificial boundaries have to be accepted. The Great Basin is so designated because it is a region of interior drainage—that is, it does not send any tribute to the sea. Its boundaries are therefore the crest-lines of the surrounding divides or water-partings. The Rocky Mountains, on the other hand, are defined as an elevated region, the boundaries of which are determined by relief and not by drainage. The basis of classification in these two instances is not the same, and one province overlaps the other. The streams flowing westward from the Rocky Mountains into the Great Basin—such, for example, as Bear, Provo, and Sevier Rivers in Utah—have their sources well within the Rocky Mountain province as defined by uplift, but yet lie wholly within the Great Basin province as defined by drainage. In spite of this inconsistency, geographers recognise as the western border of the Rocky Mountains the irregular and in part indefinite line where the elevated region breaks down and meets the broad level-floored valleys characteristic of the Great Basin. This line, or more properly belt of country, although indefinite at the south, may for convenience be taken as beginning at the head of the Gulf of California, and extending up the Colorado River for about 300 miles, to where that river makes an abrupt bend, turning southward after a westerly course through the Grand Cañon. From the locality indicated, the boundary passes through central Utah, and is sharply defined for most of the way by the bold western escarpment of the Wasatch Range. In the neighbourhood of Great Salt Lake the border of the mountain belt trends more and more to the northwest, crosses Idaho diagonally, and in northern Washington merges with or closely approaches the Cascade Mountains. In this northern region the border of the Rocky Mountains is again indefinite, and until the geological structure of western Canada is more thoroughly studied can only be located provisionally.

The unsatisfactory condition of the nomenclature at present applied to the larger topographic features of North America is illustrated by the fact that to the north of the United States-Canadian boundary the term Rocky Mountains is much more restricted than is the custom in the United States. In Canada this name is applied to the most easterly of the ranges or chains of the Pacific cordillera. This difference in the significance of the name referred to on the opposite sides of the international boundary is unfortunate, but is due in large part to our ignorance of the geography and geology not only immediately along the boundary line, but generally throughout the rugged region of the northwest portion of the continent.

One of the most important geographic features in the central part of the United States is the presence in Wyoming of a broad, generally flat, region known as the Laramie plateau (plains) and its extension westward across nearly the entire width of the Rocky Mountains. The general elevation of these "plains" is about 7,000 feet, or approximately 1,000 feet greater than that of the western border of the Great plateaus. The Laramie plateau and country to the west having a similar topography, furnished a convenient pass for the Union Pacific, the oldest of the transcontinental railroads, and divides the Rocky Mountain belt into two portions, which may be termed in a general way the northern and southern Rocky Mountains respectively.

To the north of the Union Pacific Railroad there are several important mountain groups, termed collectively the Stony Mountains by Lewis and Clark in the report of their bold explorations across the continent in 1804, but not generally used since that time. This name has recently been revived by J. W. Powell as a convenient term by which to designate this large division of the Rocky Mountain belt, but unfortunately is not recognised and has no significance to the north of the international boundary. What the natural limitations of the Stony Mountains may be in Canada remains to be determined.

The Stony Mountain system includes the Big Horn Mountains in north-central Wyoming, the sharp and lofty Teton Range to the south of the Yellowstone National Park, and several other rugged uplifts of great extent in Montana and Idaho, and should the name be extended to the north of the international boundary until a natural limit is reached, it will include the Rocky Mountains of Canadian geographers (the most eastern of the great uplifts constituting the Rocky Mountain belt), together with the several ranges of the Gold Mountains. These several mountain ranges and groups of ranges appear to have diverse geological structure, but their histories are by no means thoroughly understood. Some of them, as stated by Powell, are carved out of broad folds, and involve both originally deeply seated igneous and metamorphic rocks and upturned and folded sedimentary beds; while others are due to movements along lines of fracture and in part of overthrust.

The Stony Mountains form a portion of the continental divide which parts the waters flowing to the Pacific from those that find their way to the Atlantic. The thousands of streams tributary to the Missouri head against the equally numerous fountains supplying the westward-flowing Columbia. The broad valleys between the several ranges have a general elevation of between 7,000 and 8,000 feet, and the bold, massive mountains rise from 10,000 to over 13,000 feet above the sea. Owing to the considerable elevation even of the valleys, and the northern position of the region here considered, as well as its distance from the equalizing influence of the sea, the extremes of climate are strongly marked. The summer season is comparatively short, and in the valleys the heat is intense (ranging from 90° to 112° F.) and the rainfall small or none at all, while the winter season is cold (temperatures of from -15° to -30° F. being frequent) and accompanied by an abundant snowfall, especially on the mountains. Agriculture, although carried on in the valleys, is of comparatively small importance, and is usually dependent on irrigation. The mountains are snow-covered through much of the year, and small glaciers occur about the lofty summits of the Teton Range and on the mountains near the international boundary and in Canada. The valleys are generally destitute of trees except along the streams, where white-trunked cottonwoods spread their green leaves in summer and become a tracery of golden yellow in the autumn, marking the courses of the life-giving waters. The lower mountain slopes are covered with dark forests of pine, spruce, and juniper, which increase in density and extent as one follows the ranges northward until the influence of the high northern latitude is felt, and in northern Canada the zone of the subarctic forest is reached.

In the central part of the Stony Mountains is situated the justly famed Yellowstone National Park, which is truly remarkable for its fine scenery, its deeply carved and gorgeously colored cañons, and most of all for its numerous hot springs and spouting geysers. This is the only geyser region on the continent, and the most extensive of the three now existing in the world.

The finest scenery of the northern division of the Rocky Mountain belt lies to the north of the international boundary, and within recent years has been rendered accessible by the building of the Canadian Pacific Railroad. It is in this region that the mountains are highest, most rugged, and clothed most completely with the dark, sombre, evergreen northern forests. Here, too, high up among the bare serrate mountain tops, and mostly above the timber-line, are found the largest of the glaciers in the Rocky Mountain belt. This wonderful region of rugged mountains, deep and formerly glacier-filled valleys, impetuous rivers, and dense forests has only recently become known to the world at large. Vast areas, no doubt as attractive as those about Banff, Lake Louise, Glacier House, etc., already famous, remain to be discovered and described.

In the fastnesses of these wild northern Rockies moose, elk, deer, bear, mountain-sheep, and mountain-goat still abound. The buffalo (bison) is protected in the Yellowstone National Park, and will probably be preserved from extinction. A small herd also survives in Canada. The streams, except those flowing from glaciers, are bright, clear, and swift, and are well stocked with fish. The trout, represented by several species, there finds the cool retreats so essential to its life. To the sportsman and skilled angler the northern Rockies are a paradise. Among the lofty mountains and in the larger valleys there are many lakes, more especially in northern Idaho and Montana and in Canada. Many of these, and particularly those near the heads of the valleys and about the more lofty peaks, are true rock-basin lakes, worn out by the grinding of sand-charged glacial ice when the glaciers were far more extensive than now. The large lakes situated in the trunk portions of the broad-bottomed valleys are in many instances retained by dams of glacially deposited detritus and record the changes in the aspect of the land inherited from the Glacial epoch. These numerous lakes present a vast variety of scenery, and in many instances reflect from their placid mirror-like surfaces as beautiful and inspiring pictures of rugged grandeur as can be found in the world. The natural beauties of the classical lakes of Switzerland and Italy are rivalled by many of the charming water bodies of the northern Rockies, which but few men appreciative of the beauties of nature have ever seen.

To the south of the Laramie plateau the mountains of the Rocky Mountain system are more irregular and more lofty than those to the north of that break. The many rugged ranges in southern Wyoming, Colorado, and northern New Mexico form a great group, to which the name Park Mountains has been applied by J. W. Powell. The several ranges composing this group have a general north and south trend, to which, however, an exception is furnished by the Uintah Mountains in southwestern Wyoming and eastern Utah, which consists of a deeply dissected east and west fold or broadly uplifted plateau. Intervening between several of the adjacent ranges there are wide, nearly flat-bottomed valleys, which owe their leading characteristics to the deep filling of depressions by débris carried from the bordering mountains by the wind and streams. These broad valleys surrounded by rugged peaks are known as parks, and the numerous ranges among which they are situated are hence designated the Park Mountains. The term by which the valleys are known is in some respects misleading, as the word park usually carries the idea of a diversified and in part forested region, with mild, picturesque scenery. Perhaps a city park or the beautiful rural estates of England are most usually brought to mind when the term referred to is mentioned. But in the great mountains of the central portion of the continent one's idea must expand to keep in harmony with his surroundings. The natural parks of that region are broad, generally treeless, valleys with winding streams, the uplands are grass-covered and rolling, and in distant views the courses of the streams are marked by narrow belts of verdure. The picture is framed by a succession of mountain domes and embattled cliffs. Over all arches the dark blue, cloudless sky of a nearly rainless region. In the clear air distances are deceptive, and what appear to be miles to the novice must be extended to leagues in order to acquire adequate conceptions of the magnitude of the scene.

The most famous of the great tracts of generally level land surrounded by the high ranges of the Park Mountains is San Luis Park, situated in southeastern Colorado and extending southward into New Mexico, which has a length from north to south of about 130 miles, and is from 20 to nearly 40 miles wide. Its general elevation is between 7,000 and 8,000 feet. This great valley, level-floored with soft deposits swept in from the bordering highlands, and almost completely surrounded by rugged mountains, although more desolate than the majority of the numerous similar valleys in the same region, is typical of its class. The Rio Grande winds through its entire length and many streams rising in the bordering mountains flow to the valley during the winter season, but in summer, owing to the high temperature, active evaporation, and small rainfall, only a few of the larger of these mountain-born torrents reach the main, southward-flowing river. In the southern portions of the valley large areas are covered with drifting sand, which is fashioned by the winds into ever-changing dunes of a creamy whiteness. Some of the streams from the mountains expand on the plain and form the San Luis lakes, from which the water escapes by evaporation, thus causing them to become alkaline. The land bordering the lakes is whitened as with snow by saline incrustations. On the lower portion of the rim of this mountain-inclosed basin there are scattered groves of pines and junipers, and at higher elevations the mountains are dark with forests. The more lofty peaks, however, rise far above the upper limit of the forests and are rugged and magnificent even under the glare of a cloudless sky.

To the east of the San Luis Park, and rising about 7,000 feet over it, and over 14,000 feet above the sea, stands Sierra Blanca, one of the finest of the many majestic mountains of Colorado. In summer immense cloud banks frequently gather about this cold, isolated peak, and local storms, accompanied by fierce lightning and echoing thunder, beat upon its shrouded sides. These tempests raging on the mountain top, while the adjacent valleys are flooded with sunlight, recall the scriptural accounts of the storms of Mount Sinai. In fact, the southwestern portion of the United States and the adjacent region in Mexico, so far as scenery and climatic peculiarities are concerned, have much in common with Palestine.

The other great parks in Colorado, which have suggested a name for the group of mountains in the midst of which they are sheltered, are less arid and less desert-like than the one just described; but like it, derive their magnificence and fascination from their vast extent, the sublimity of the bordering mountains, and the wonderful transparency of the air above them, rather than from the topography of their nearly level floors or the vegetation that strives ineffectually to clothe their nakedness.

The individual summits as well as the separate ranges composing the Park Mountains are remarkable for their massiveness and the great height of their bare rounded summits rather than for picturesque details. Several of the peaks are among the highest in the United States. One conspicuous feature is the considerable elevation of the valleys, usually over 7,000 feet, and the large number of lofty summits. Of the peaks that have been measured, over 30 exceed 14,000 feet in height. The portion of the Park Mountains above an elevation of 10,000 feet, as is indicated on the map reproduced on page 65, is far greater in area than any other region of similar altitude on the continent.

In the Park Mountains, and generally throughout the southern Rockies, even to central Mexico, the forms that meet the eye are the remnants of vast upheaved folds and domes of the earth's crust sculptured and degraded by erosion. The nearly horizontal rocks of the Great plateaus on meeting the eastern border of the mountains are bent abruptly upward, and in many places stand on edge or have been overturned so as to dip westward. This abrupt upward bending and the presence of remnants of the same beds on the summits of some of the higher mountains shows that the strata have not been simply folded into anticlinals and synclinals, but that there has been a thickening and upswelling of the rocks beneath.

In the northern Rockies, except in western Idaho and adjacent portions of Washington and Oregon, evidences of recent volcanic activity are rare, although igneous rocks cover great areas, and in the Yellowstone Park numerous geysers and hot springs bear evidence to the presence of abnormal heat in the earth's crust. In the southern Rockies, however, volcanic mountains which still preserve their forms are numerous in certain regions, and in Mexico there are mighty volcanic piles and many lesser elevations built up by extrusion of molten material, some of which are still active. Examples are furnished of volcanic mountains ranging from perfect cones with curved slopes typical of the forms produced by the piling up of various sized fragments about the vents from which they were extruded, to irregular serrate peaks which reveal the anatomy of the dissected volcanic masses, and even the dikes which remain after the surface elevation of a volcano has been removed. The most modern volcanoes in this great group of mountains are situated in central Mexico, but others nearly as perfect in form occur in New Mexico and Arizona, and in the plateaus to the east of the Park Mountains. The Spanish peaks in southeastern Colorado are instructive illustrations of the topographic forms produced when a volcanic mountain has been deeply dissected.

In the formation of volcanic mountains there is an extrusion of molten and fragmentary material accompanied by an escape of great volumes of steam at the surface. Closely related to this phase of vulcanism is the injection of molten material into the earth's crust from below, so as to force its way between stratified beds and produce intruded sheets. In this latter process the sheets of injected material may be thin in comparison to their lateral extent or thick lens-shaped masses. In the production of either of these forms of intrusion the cover above the injected material is lifted and a change is made in the topography of the surface. The intrusions, which are thick in comparison to their lateral extent, are known as laccoliths. At times intrusions of this nature are of such thickness that they produce true mountain forms. If unmodified, these elevations would be domes, but when their surfaces are broken by erosion and their dissection and removal progresses they frequently assume rugged, serrate forms.

The type of laccolithic mountains made known some years since by the studies of G. K. Gilbert is furnished by the Henry Mountains, in southern Utah. More recently it has been found that this interesting phase of mountain building is illustrated by many other examples in the Rocky Mountain region and elsewhere.

The rocks exposed at the surface in the southern Rockies, as in the northern division of that great chain, embrace almost every variety which enters into the composition of the earth's crust. The central cores of many of the now deeply eroded ranges consist of granite and other similar rocks, and are surrounded by sedimentary beds which range in age from the oldest stratified rocks now known to the youngest. Igneous rocks in great variety and in all forms incident to an extruded or volcanic and intruded or plutonic origin are present. The many disturbances that have occurred have led to the formation of mineral veins and the impregnation of rock masses with ores of various kinds—such as gold, silver, lead, copper, etc.—which have been mined with great success at many localities.

The High Plateaus.—To the west and south of the Park Mountains, and situated in the western portions of Colorado and New Mexico, eastern and southern Utah, and northern Arizona, there is an extensive region having a general surface level of 6,000 to 7,000 feet above the sea, known as the High plateaus. This region has suffered great erosion and is deeply trenched by stream-carved cañons. Although not mountainous in the ordinary acceptance of the term, its surface is rugged and difficult to traverse, particularly on account of the deep cañons that intersect it in every direction.

The High plateaus are a part of the Rocky Mountain region and bear a somewhat similar relation to the Park Mountains that the Alleghany plateau does to the Appalachian Mountains. Streams flowing westward from the Park Mountains and from the southwestern portion of the Stony Mountains unite to form the Colorado River—the one great drainage channel of the region. The importance of this remarkable river in the history of the land has led to the adoption of the name Colorado plateau by Powell and others for the region under consideration. As with so many of the grander geographical units of the continent, the precise limits of the one here considered are difficult to define; but in spite of this uncertainty as to meets and bounds, the now classical writings of Newberry, Powell, and Dutton especially have shown that a strange and wonderful land exists in the southwest part of the United States, which is of unusual interest to geologists and geographers.

The High plateaus are underlaid by nearly horizontal rocks. The larger elements in the structure are great blocks of the earth's crust measuring some 60 to 100 miles on their various borders, which are bounded by breaks (faults), or by what are termed monoclinal folds or a change from one plateau to another by a single bend in the strata. The rocks in each of the separate plateaus are usually gently tilted. Their eroded edges stand as lines of massive, gorgeously coloured, and frequently fantastically sculptured cliffs. These cliffs, when seen from below, appear as rugged mountain ranges, but to an observer standing on their deeply sculptured crests are easily recognised as the upturned edges of large gently tilted blocks of the earth's crust.

The basement rocks beneath the High plateaus are very ancient granites, schists, etc., which formed a land surface and were greatly eroded before the first of the superimposed stratified beds were deposited upon them. The first of the sheets of sediment laid down by the primeval ocean belong to the oldest rocks containing records of life that have as yet been recognised—the Algonkian (pre-Cambrian) terranes of modern geology. Above these come other deposits of sandstone, shales, limestone, etc., representing a wide range of geological history, and including as the upper member of the series the sediments of large Tertiary lakes. This vast succession of stratified rocks, some 13,000 feet in thickness, has been upraised in a broad way, without the crumpling and folding, but broken, as stated above, into great blocks which are now variously inclined, but still preserve a plateau-like character.

Besides the movements in the earth's crust which raised the plateaus and caused fractures and simple or monoclinal folds in the rocks of which they are composed, there occurred volcanic eruptions which produced numerous cinder cones, extensive lava-flows, and widely spread sheets of comminuted material known as lapilli, dust, and so-called ashes.

Although the history recorded in the rocks forming the High plateaus is one of fascinating geological interest, the easier and more obvious lesson that the region has to offer, more especially to the geographer, has been engraved and etched on its surface by streams and wind-blown sand.

On the High plateaus the rainfall is comparatively small, and the streams originating there mostly ephemeral. But on the mountains to the east and north the precipitation is more abundant and rivers are formed which flow across the plateau region. The Green and Grand Rivers, fed by many tributaries, unite to form the Colorado, which flows southwestward for some 700 miles and discharges its muddy waters into the Gulf of Lower California. This great river year by year and century after century has deepened its channel through the plateau region where the rainfall is small, more rapidly than the general surface has been lowered by erosion. The main conditions are a broad area of nearly horizontal rocks, raised high above the sea or above the base level of erosion, and an arid climate; crossing this region is the ever-flowing river, which, acting like an endless saw, cuts deeper and deeper into the blocks of the earth's crust which have been raised athwart its course. Resulting from these conditions is a mighty trench or cañon, which is by far the most magnificent of its kind in North America, if not in the world. Not only has the main river sunken its channel into the earth to a depth of more than a mile throughout a large portion of its course, but each tributary stream has been engaged for a long period of time in a similar task. Although most of the streams originating on the surface of the plateaus are ephemeral, they work rapidly when the occasional heavy rains flood their channels. This deepening of the stream channels, while their borders and the intervening portions of the plateau surface suffered but comparatively slight erosion, has produced a wonderful system of deep steep-sided trenches in the borders of which the edges of the dissected rocks are exposed in nearly vertical precipices.