Pl. 10. View of the Deerfield gorge from the east summit of the Mohawk Trail.
The high level flat to the extreme right and extreme left is the New England peneplain. The terrace bordering the steep walls of the gorge is a strath.
The road crosses a series of strath heads, which drain into the Cold River, and ascends to the west summit (33.2). At first it seems possible to throw a stone into North Adams, so abrupt is the western slope. The city lies deep in a limestone valley, and beyond it the Taconic ranges rise steeply west of Williamstown, over six miles away.
On the long descent into the valley, the roadway is cut into albite-biotite schists with horizontal cleavage. Above and below the sharp hairpin turn (35.2), there is a beautiful view to the south along the strike of the limestone trench and along the route (State Highway 8) which is to be followed from North Adams (37.8) to Adams. Not far south of North Adams the road passes the west portal of the Hoosac Tunnel (39.4). Boulders on the mountainside east of the highway are glacial erratics which were left above the level of the valley trains and above the surface of glacial Lake Bascom. The limestone which outcrops on the slopes of Mount Greylock west of the road is used for lime (41.6), and the quarries provide ideal exposures for a study of the rock. The burning plant (42.2) is at the roadside. The road branches in the center of Adams (43.6), one route (State Highway 116) continuing ahead to Savoy and Plainfield, the other veering right to Mount Greylock, Dalton, and Pittsfield.
The Savoy road follows a broad valley eastward into the hills. A perceptible steepening of the slope occurs where it crosses from the dolomitic limestone below, to the albite-biotite schist above, at a thrust fault (47.5). Hard white Cheshire quartzite (48.2) and arenaceous limestone (49.0 to 49.6) overlie the schist and outcrop by the roadside, and in places the arenaceous limestone has weathered to a white glistening sand.
The road soon drops into a wide and open valley (50.1) which seems to slope interminably southeastward; this is the head of the Westfield drainage, and it has occupied this position in the Westfield system far back in geologic time (see p. 14). The little village of Savoy (51.8) nestles near the eastern edge of the valley, and once beyond the settlement, the highway tops a divide (52.7) comprised of rolling hills. It skirts Plainfield Pond (56.0 to 56.4) and then comes out upon a panorama of the upland which embraces the entire Westfield basin (57.5). This section is underlain by the Savoy schist, which is characterized by its many large red garnets. At the hilltop (59.7) in Plainfield the road forks, the route to the right descending to the Berkshire Trail and the road ahead proceeding to Ashfield. This portion of the New England upland lies so far back from the main streams that the small tributaries have not yet cut deeply into its gently rolling surface, and no hint of hidden valleys can be detected in the peaceful landscape.
The Ashfield road traverses woodland country that is almost flat. The stream valleys are broad and are rarely more than a hundred feet below divides. Even Swift River (63.9), which crosses the road about two miles above the end of its entrenched gorge, has not deepened its valley, despite the long span of years since New England was raised to its present elevation (see p. 47). Past the alternate road to Cummington (64.0), the route continues across the flat country above Ashfield; but where the road to Goshen turns south (66.4), deep dissection of the New England upland begins. An opening in the trees (66.6 to 67.1) discloses the valleys along the South River in the vicinity of South Ashfield, as well as the level skyline in the highlands east of the Connecticut Valley. The road drops into the South River valley at Ashfield (68.2), where a choice of routes to Greenfield is presented. The road that follows the South River to Conway (75.4) is the more interesting.
The river is joined by a tributary from the north at South Ashfield (69.9), and the streams occupy deep but open valleys. Kame terraces flank the rivers and are a source of gravel for road ballast. The old dam (73.9) near Conway is a picturesque spot, and the deep, shady pool below is not neglected by anglers. Glacial erratics (see pp. 8-9) dot the hill slopes, but ledges are rare and consist of the locally named Conway schist where the rock does appear at the surface. The road branches again at Conway: the left fork goes north along the dissected brink of the Deerfield gorge to Shelburne Falls, but our choice falls upon the eastward route to South Deerfield.
The highway climbs through a cut (75.8) in contorted, gneissic Conway schist, which seems to be lined with twisted white quartz veins from this point to the margin of the Connecticut Valley. The road levels off just before it reaches the New England upland, and then it drops through rolling hill country to the shaded valley of Mill Brook (77.4), which it follows to the edge of the lowland (80.1). Rocky ledges are common along this swiftly flowing stream. A good view of the Pocumtuck Hills appears on the left (79.7), with the flat plain of the old Deerfield delta stretching to their base. The road crosses this plain and enters South Deerfield (81.8).
The tour turns north on Federal Highway 5, which is built on the deposits spread in glacial Lake Hadley by the Deerfield River from its mouth eastward to the foot of the Pocumtuck Hills of Triassic conglomerate. Bloody Brook (82.2) drains this part of the plain. North of the road which goes through the notch between the Sugarloafs (82.6), the delta deposits continue as a terrace along the base of the Pocumtuck Hills as far as Cheapside. But the Deerfield has excavated its post-glacial delta, and the roadway descends to the meander-cut floodplain (84.4 to 88.1), though it rises over one of the meander scarps (85.1). Remnants of the Deerfield delta form a terrace due west across the valley and on the margin of the hills. The entire lowland north of the meander-cut terrace was inundated in 1936, and the water level may still be identified by debris on the railroad embankment on the right. Old Deerfield (86.1) itself is on a meander-scarp terrace, and the 1936 flood line is well marked along it. After the road crosses the Deerfield River (88.3), it leaves the floodplain as it climbs to the center of Greenfield (89.8).
Route 2 also leads eastward from Greenfield to the French King Bridge and Millers Falls. The highway out from Greenfield turns north (0.3) along the west front of the trap ridge, near the summit of which several individual lava flows are represented by separate sets of columns superimposed one upon the other (see p. 26). The underlying bedded sandstones outcrop in the lower wooded slopes. A road branches right (1.7) to Turners Falls and crosses the lava ridge, but the main highway continues straight to a sharp curve near Falls River (3.4). Pillow-shaped masses of lava characterize the bottom of the lava flow and lie above conglomerate in the bluff to the right. The valley of Falls River is a fault zone slicing across the lava sheet, which reappears at the lookout-parking place at Turners Falls (3.5). The extent to which the waterfall has receded (see pp. 58-59) may be judged from the length of the gorge.
The route continues left past the bridge entrance (3.6). Ripple-marked red shales—once Triassic muds in which stray dinosaurs left their tracks—outcrop by the roadside (4.6 to 5.7), and coarse conglomerate beds (5.9) overlie the shales and dip steeply towards the river. Somewhat farther east a broad sand plain (6.0 to 6.8) of glacial outwash (see p. 59), which ends at the French King gorge, buries the Triassic bedrock, but once again conglomerate appears and forms the west wall of the gorge. Pre-Triassic crystalline rocks (6.9) likewise outcrop on the western cliffs, and form a narrow ridge between the present course of the river and the pre-glacial channel, which lies below the glacial delta (7.0 to 7.9) of Millers River.
The road to Northfield turns left (7.9) and another (8.7) leads right to Millers Falls, but Route 2 continues east, climbing high above the river (9.9), which flows through a narrow gorge. Gneiss with horizontal banding outcrops (11.2) in mesa-like hills north of the highway, which descends to a point (12.5) that was 5.5 feet under water during the 1936 flood. The road continues near the water’s edge for almost half a mile, and the narrow gorge through gneiss ends at Erving (13.8). Here the valley widens out into a hilly lowland which has been developed on schist with occasional bands of gneiss. The road follows the north bank of the river across this lowland to Orange (17.9). Route 2 continues to Athol where the Daniel Shays highway enters from the south, but an alternate route, which turns right in the center of Orange and crosses Millers River (18.0), provides a preferable short-cut to the Daniel Shays Highway (21.8). This section of road is lined with stone fences which memorialize the combined labors of the great Ice Sheet and the early settlers.
Route 32 from Petersham and Worcester enters from the left (22.7) just before the highway dips into the creek bottom at the edge of the Quabbin basin. Thence it ascends to the New England upland level, where a lookout (25.5) affords an expansive view to the east and north, with Mount Monadnock rising prominently on the distant skyline. New Salem (25.8) is on the hilltop. Hornblende schist outcrops at intervals across the broad ridge, and especially near the descent (28.4) southwestward to another stream (30.3) which empties into the Quabbin Reservoir. Once again the highway climbs rather steadily for three and one-half miles, passing the Shutesbury road (31.0) on the right, until it reaches another lookout (34.6) from which the trenched New England upland spreads out to the east. Pelham gneiss is the main rock on the broad ridge west of the Quabbin basin, especially in the vicinity of Pelham (35.2), which gave the rock its name.
The tour turns east to Amherst (41.7), following a section which has been described elsewhere (see pp. 78-79). The principal sights include the panorama of the Connecticut Lowland and the ice-margin lake deposits. The drive from Amherst to Northampton (see pp. 78-79) and from Northampton to South Deerfield (see pp. 87-88) on Federal Highway 5 has likewise been covered in other tours, but some new features may be seen along the shorter route from Amherst to Sunderland.
The Sunderland road turns right at the north end of the Amherst common. It descends, first, from Amherst Island, in glacial Lake Hadley, to the old beach at Massachusetts State College (42.6), and then from the beach to the lake bottom (43.2) north of the campus. The route takes the left fork in North Amherst (44.2), traverses part of the old lake bed, swings west around the Long Plain delta (45.5), and crosses its entrenched brook (46.1). Most of the stream’s water seeps through the delta sands and gravels, and emerges in springs at the Fish Hatchery (46.3). Gravel pits across the road furnish an excellent section of the fore-set and top-set beds of the delta. The road right (46.8) goes to the delta top east of Mount Toby, Montague and Turners Falls, but the main highway continues north.
The road turns left and then right (47.2), cutting through a beach bar in glacial Lake Hadley, and passing a sand dune area (47.6) which developed from the sandy braids in the channel of the Connecticut when it first established its course on the lake bed (see pp. 4-6). The route drops down from a terrace (47.9) to the highest floodplain level of the Connecticut. Swales (48.3 and 48.5) on this flat represent former river channels, and the scalloped embankment to the east records the lateral swing and undercutting of the meandering river. The North Hadley road (48.7) enters from the south along a low ridge between two swales, and after the sharp right turn into Sunderland (49.2), the road divides, one fork going north to Montague, the other west across the Sunderland Bridge to South Deerfield.
The Sunderland Bridge (49.4 to 49.6) offers a good view downstream along the natural levees (see p. 2) and westward to the cliffs of Mount Sugarloaf (see pp. 56-58). The road rises above the floodplain (49.9) and passes the Sugarloaf trail (50.0) on the right. A right turn into Federal Highway 5 at South Deerfield (51.0) brings the motorist back to a section of country already described in connection with the Mohawk Trail tour (see pp. 95-96), and another eight miles of driving brings him to Greenfield (59.1).
A variant of the drive east from Greenfield is available in the route that turns right across the Turners Falls Bridge (3.6 to 3.8) and follows the east side of the Connecticut Valley southward. The road turns left in the center of Turners Falls (4.2) and climbs the embankment which the river excavated in the old lake beds. On the sand plain above (4.9), the left fork goes to Millers Falls and the right, to Montague. The Montague road skirts the west side of a low line of hills which terminate at a depression (8.6) on the pre-glacial course of the Connecticut. The road goes over Saw Mill River (9.4), in the bed of which Triassic conglomerate is exposed. Conglomerate also appears in the hills directly south, but the older crystalline rocks crop out in an exhumed ridge to the southwest and in the highlands eastward. The conglomerates form the south end of a Triassic basin extending from Mount Hermon and Northfield farther up the valley (see p. 26). Beyond Montague (9.7) Triassic conglomerate appears along the roadside (10.1) as far as the forks to Sunderland and Millers Falls (10.8).
The Millers Falls road follows the foot of a terrace which rises to the old delta level, and at the next fork (11.0), the route keeps right and continues southward to North Amherst. The delta of the glacial stream buried many ice cakes which left numerous kettle holes (11.0 to 11.5) when they melted. The stratification of the deposits is displayed in the many road cuts. The route crosses the Central Vermont Railroad (11.5) and follows an old outwash plain southward past the road to Roaring Brook (13.1) (see p. 54). The tour continues through a narrow stretch in which crystalline rocks predominate, as far as the Long Plain delta (15.6). Mount Toby rises steeply on the west side of the railroad. A third of the way up the mountainside can be seen (13.9) a conspicuous bench, which consists of an exhumed remnant of the ancient, sloping granite mountain front on which the Triassic sediments were laid (see pp. 20-21). The bench level drops northward to the railroad at Roaring Brook, and southward it crosses the road (14.9). The conglomerate east of the road (14.9 to 15.3) fills an old mountain valley. A road east (15.3) goes to Leverett, and the lead vein is located just south of it at the hilltop.
The route skirts the margin of the crystalline rocks and crosses the railroad again (15.6). Just beyond the road to Leverett station (16.1) the motorist may exercise the option of returning to the Sunderland road (17.3) by going right across the Long Plain delta and thence to Greenfield (29.6) via South Deerfield (see p. 95). Or he may extend his trip by taking the left fork of the Mount Toby road, which follows the boundary between the Long Plain delta and the glaciated eastern highlands. Boulders and bare ledges feature in the landscape to the east, whereas the flat delta and the level beach margin (17.9) lie to the west. Beyond the limits of the delta lies a series of bare ledges of gneiss. After crossing Factory Hollow Brook (19.1), the route joins the Sunderland road (19.2) at the center of North Amherst, returning to Greenfield (34.1) by way of Sunderland and South Deerfield, as before (see p. 98).
The Sunderland road (10.8) just beyond Montague turns right and climbs the terrace along the floodplain of Saw Mill River. The plain is the delta which this stream built into Lake Hadley. A few rock ridges project above it; buried ice has melted to form kettle holes (11.4) (see pp. 7-8); and post-glacial streams have cut valleys in it; yet it preserves its deltaic form to the old lake margin (11.6). Low shed-like cliffs occur east of the road (11.9); the overhanging rock is Toby conglomerate, and the excavated shelter is a gray shale which was laid in a Triassic lake bed (see pp. 22 and 68). These cliffs recede from the highway and end (12.3) at the Sunderland Caves (see p. 55). The route continues downhill and joins the river road on the floodplain of the Connecticut (14).
The road rises over a promontory (14.1) formed by the resistant Deerfield lava sheet (see p. 26) and then descends to the river floodplain and meander-cut terraces (see p. 22), which cross to the east side of the highway and continue south beyond Sunderland (15.5). In Sunderland junction is made with the longer tour through Amherst (see p. 98), and the return to Greenfield may be made by that route (25.4).
In the vicinity of Springfield the most interesting drives are to be found on the west side of the Connecticut River, for the comparatively flat land east of the river is thickly settled and heavily industrialized, and geological phenomena are effectively masked. The country to the west offers a display of features which may be traced to the activities of the river, to the former presence of glacial Lake Springfield, to the prolonged erosion of the Triassic bedrock, and to the resistance of the pre-Triassic rocks in the western highland. Almost any trip will include this entire suite of geological phenomena. The distances which are given in the following tours have been taken from the west side of the North End Bridge.
This route follows north on the floodplain along the river bank via Federal Highway 5, and the heavy retaining wall is designed to keep the river out. The sand promontory which comes to the left side of the road (0.6) is a remnant of the old lake—bottom deposits. Past the junction with the road through West Springfield (0.8), the highway utilizes the old lake beds, which form a terrace above the present floodplain; but ultimately (1.6) it drops again to the floodplain level, with its many abandoned channels, although it discreetly stays on one of the higher, and older, meander-cut terraces. A cut-off to Chicopee turns right (2.4), but Federal Highway 5 continues north across the meander terraces to the forks (4.6) which lead to the residential (left) and business (right) sections of Holyoke.
Here the main highway climbs steeply from the floodplain to the top of the lake deposits. The view north shows the Holyoke Range rising above the roofs and chimneys of Holyoke. Lake deposits form a broad flat between the Triassic volcanic ridges which lie to the west and the trench cut by the Connecticut River.
The road from Westfield and the airport (Federal Highway 202) from the left, and the road to Easthampton (7.6) turns left from the main highway, which continues north. The north route, described under the tours from Northampton (see pp. 80-82), features the dinosaur tracks and the succession of Triassic rocks. The Easthampton road goes past the south end of the Mount Tom Range, and its scenic attractions have been dealt with elsewhere (see p. 85). Its most interesting sights are the line of lakes between the two volcanic series and the view from the summit of the ridge. Easthampton (12.7) lies on the old lake bottom, from which an impressive view of the palisade of massive columns comprising the tilted lava flow of Mount Tom can be obtained.
At Easthampton the tour turns south on the College Highway (State 10) towards Southampton and Westfield. The road follows the gravel plain which was spread into Lake Hadley by streams flowing out of the western highland. The plain is dissected locally by the Manhan River (15.2 and 18.0) which crosses the road twice, and one small valley near Southampton (17.1) discloses Triassic arkose buried by the sand. The road rises above the lake deposits (17.4) near the Manhan River, and at once glacial erratics become numerous. The “land of stone fences” forms a narrow divide between the Lake Hadley basin and the Lake Springfield sand plain (21.1), which extends south to the valley of the Westfield River. The Holyoke road (22.5), which enters from the left, came over the trap ridge and across the lake plain.
As the College Highway approaches the edge of the Westfield valley (23.6), it slopes steeply down to the level floor cut by the river. It crosses the Westfield (24.5) and comes to the junction (24.9) with the Jacob’s Ladder route (Federal Highway 20), which offers another interesting sidetrip into the Western Upland.
The route continues south to the center of Westfield (25.2), leaving the College Highway at the south end of the common. The Springfield road goes around the central square and starts east in the valley which the meandering Westfield River carved out of the Lake Springfield sediments. The terrace levels and the scalloped pattern of the meander scarps are conspicuous along the lowland. The highway crosses the Little Westfield River (26.1) and then the Westfield itself (27.0) just beyond the entrance to Robinson State Park.
Most mineral collectors will instantly recognize a road turning off to the left (27.8) as the way to the Westfield trap quarry. For years this locality has been as important a source of specimens to collectors as it has been of crushed rock to road-builders. Beyond the quarry road the valley narrows, and the terraces close in as the river enters the gap in the trap ridge. The black lava flow crosses the river (28.3) at the Westfield-West Springfield town line, and shortly the upper flow appears, resting on red shales in both railroad and road cuts (29.1). Actually there are two flows separated by an amygdaloidal band in the upper lava series at this place. The highway crosses the Boston and Albany tracks (29.3) and leaves the river. After passing the junction with the Holyoke road (31.0), the highway drops to the upper terrace level on the bed of glacial Lake Springfield (31.4). The upper terrace is narrow here, and the road soon descends to the meander-cut terraces of the floodplain (32.1). The road to Memorial Bridge turns right (32.3) and our route returns to the North End Bridge (32.8).
This is a short drive of 5.7 miles each way from Westfield, with a mile walk from the Little Westfield road to the marble quarry. The view of the Little Westfield gorge and the entire Connecticut Lowland from Meriden to Amherst makes this trip well worth taking.
The tour leaves Westfield on the Jacob’s Ladder road and soon reaches the terraced margin (1.6) of the Westfield valley. The numerous benches along the stream banks represent temporary flood-plain levels of the Westfield. The route turns left from the Jacob’s Ladder highway (4.0) and parallels the base of the western highland to the Little Westfield road (4.9). Throughout this distance the marble quarry derrick appears on the highland skyline. Our road turns right at the next crossing and winds along the edge of the Little Westfield gorge (see pp. 61-62). The narrow hill road to the marble quarry turns right (5.7), but it is inadvisable to drive. The walk is an easy one, and the view at the top is worth the moderate physical exertion.
It must be plain, even to the casual reader, that the foregoing pages have been written with self-restraint. Many of the luring side roads were passed without so much as a pause; trips to the Cobble Mountain Reservoir west of Westfield, and to the Quabbin Reservoir east of Belchertown have not even been suggested; some of the main highways were slighted. For anyone who knows the byways and the hidden beauties that can be found in reasonably accessible places, this chapter will seem inadequate and incomplete.
But it would take a volume far beyond the scope of this brief guide to do justice to the scenery, the geography, and the geologic detail of the Connecticut Valley and its bordering uplands. The authors can merely ask the indulgence of those who would like to know more.
Travelers are inveterate collectors of mementos, and those who travel up and down and across the Connecticut Valley and who delve into its geologic history may well be interested in gathering records of its past. The best records are not in notes or printed pamphlets—not even in this volume on the subject; they are to be found imprinted in the rocks and minerals themselves. But the value of records is measured solely by their utility, and utility is achieved by systematic arrangement. So the authors will venture a few suggestions on collecting and arranging the minerals and rocks which are present in the valley and in the bordering uplands.
One mineral may come from a vein, which is the record of a fissure beneath a hot spring; another comes from a dike, which was a molten igneous rock. This specimen is a conglomerate or consolidated gravel washed into place by an ancient stream; that is a slate which was transformed from clay by intense squeezing and shearing. And if these four specimens were to constitute the nucleus of a collection, the need for classification is apparent. The first two are minerals, which are substances of limited chemical composition and well defined physical properties. The last two are rocks, which are aggregates of minerals or of mineral grains. And the minerals may be further classified according to their separate modes of origin. So, too, with the rocks. Their mineral composition indicates some of the conditions which existed where the minerals originated; the shapes of the mineral grains reveal the process which moved them to their present site; and the arrangement of grains discloses the conditions existing during aggregation at this new locality. Mineral make-up, size, shape, and arrangement of the grains provide means of recognizing major rock varieties—namely, sedimentary, igneous and metamorphic types,—and also of reading each rock’s history.
The vein minerals, which are deposited in conduits for hot spring water, commonly possess attractive crystal forms; they include barite, quartz and amethyst, fluorite, calcite, datolite, galena, sphalerite, pyrite and others almost too numerous to list. Almost equally attractive crystals may be obtained from some metamorphic rocks, in which they have formed as heat and pressure abetted the growth of certain minerals at the expense of their less favored fellows; this group contains garnet, kyanite, chlorite, amphibole, epidote and many others. Less spectacular are the minerals resulting from the decay of rocks by percolating surface water, such as kaolin, limonite, some calcite, and the bright-colored copper carbonates. Two additional types of minerals are formed as the result of normal sedimentary and igneous processes, which will be described at length in connection with these two kinds of rocks. So, after the rock specimens are sorted from the minerals, the latter may profitably be arranged into five groups:
The mineral list which follows is far from complete; it contains only those minerals which are most commonly found in casual visits to the localities discussed in connection with the local tours of the Connecticut Valley. Additional species are listed and described in any textbook on mineralogy.
QUARTZ is a hard, white or colorless mineral which will scratch glass easily. In the technical language of the crystallographer, crystals are hexagonal or six-sided prisms, terminated by hexagonal pyramids; and the six flat faces which make the sides, together with the six triangular faces which form the apex, are readily recognized. Massive forms break with a curved or conchoidal fracture and were used by the Indians to make arrow-heads. The mineral is very abundant in all the lead veins and trap quarries; and in some of the latter, specimens of the purple variety of quartz, amethyst, are common. A black, smoky variety has been discovered in the pegmatite dikes of the highlands. Chemically quartz is the dioxide of silicon (SiO₂).
CALCITE breaks along three smooth surfaces or cleavage planes. Each surface is rhomb-shaped, and the six rhombic faces fit together into a characteristic rhombohedral form. A knife will scratch the mineral easily. Calcite is abundant in the white veins of the trap quarries and is the principal constituent of the crystalline limestones in the Hoosac Valley between North Adams and Pittsfield. Calcite is a carbonate of lime (CaCO₃).
BARITE resembles calcite because it can be scratched with a knife and has three smooth cleavage planes. It differs in having one cleavage perpendicular to the other two, which intersect at angles of 78°. The mineral is more than four times the weight of an equal volume of water, and it feels heavy. It is found in the lead veins at West Farms, Hatfield and Leverett. In large quantities it has commercial value as a source of the element barium, for it is the sulphate of barium (BaSO₄).
GALENA is the chief metallic mineral in the veins at Leverett, Hatfield and Loudville. It is very heavy and has a metallic gray color; it breaks into perfect cubes. A knife scratches it easily and crumbles it to a black powder. The mineral is a lead sulphide (PbS).
SPHALERITE is a lustrous, resinous brown mineral in these same veins. It cleaves into multi-faced fragments and is softer than a knife. Chemically it is the sulphide of zinc (ZnS).
PYRITE is the deceptive golden-colored, metal-like mineral which has earned the name of “fool’s gold.” It will scratch glass, and it crushes to a black powder. The materials in it are iron and sulphur (FeS₂).
CHALCOPYRITE resembles pyrite but will not scratch glass and has a greenish yellow color. It is a compound of copper, iron and sulphur (CuFeS₂).
The veins in the Connecticut Valley region contain many other minerals, among which must be mentioned datolite, natrolite, apophyllite, thomsonite, fluorite and babbingtonite in the lavas; and siderite, rhodochrosite, rhodonite, wulfenite and pyromorphite in the older veins of the highlands.
The minerals found in pegmatites are legion. More than thirty can be collected on any trip to Collins Hill near Portland, Connecticut, or to the Ruggles Mine near Grafton Center, New Hampshire. Only the minerals appearing most commonly in pegmatites are described, but a list of others is appended as an aid in consulting a textbook. Igneous rocks contain practically the same suite of minerals as pegmatites, but in smaller grains.
MICROCLINE is a white to flesh-colored feldspar with two almost perpendicular cleavages. It will scratch glass or a knife. One cleavage face shows a grid of translucent and transparent lines intersecting at 90°.
ALBITE is the second most abundant feldspar. It is white and may generally be recognized by its two cleavage surfaces at 86°. Its growth may be likened to piling a series of plates with their surfaces parallel to one of the cleavages; during growth the plates are laid alternately face up and face down, so that the 86° cleavage edges zigzag in and out, forming a surface which, on the average, is perpendicular to the growth cleavage surface. The separate plates can usually be detected as fine bands or striations. The mineral scratches either glass or a knife.
MUSCOVITE is the white mica found in tabular crystals that can be cleaved into flexible and elastic sheets. It can be scratched and cut easily with a knife or shears.
BIOTITE is an amber-colored to black mica. Like muscovite it is flexible and elastic, but it is slightly more brittle.
TOURMALINE crystals occur in triangular prisms with the corners bevelled so as to give them a rounded appearance. They lack cleavage, are very brittle, and will scratch glass. Black is their usual color, but red and green varieties are present in many pegmatites.
SPODUMENE crystals are white to pale rose in color, and they occur as flattened prisms with bevelled corners. They cleave parallel to the surfaces bevelling the corners. The mineral is much harder than a knife, and the cleavage surfaces have a lustrous, slightly satiny appearance.
RADIOACTIVE MINERALS occur in many pegmatites and metamorphic rocks of this region. The species which have been formed as a result of recent alteration are brilliant golden or green encrustations in cracks or on a pitchy-black nucleus. The most abundant ones are uranite, autunite and torbernite. Older primary or source minerals are pitchy-black and are surrounded by a narrow rusty red zone or “halo,” ¹/₁₆ to ⅛ inch wide; an elongate species resembling a rusty hand-made nail is allanite; the more pitchy, irregular-shaped mineral is usually uraninite or pitchblende.
Other minerals found in pegmatites in the Connecticut Valley region include beryl, apatite, zircon, garnet, fluorite and lepidolite.
Most of the minerals in normal igneous rocks are too minute to be recognized easily, but a few have distinctive characteristics which serve to identify them. QUARTZ is a hard, dark, glassy-looking mineral without cleavage. ORTHOCLASE and MICROCLINE feldspar are hard, flesh-colored (occasionally white) minerals with flat cleavage surfaces. The minerals making the white lathlike mosaic on the weathered surface of the Range at the Mount Holyoke House are LABRADORITE feldspar. They are about ¼ inch long and ¹/₅₀ inch thick—too small to permit testing by ordinary physical methods, although unweathered pieces have essentially the same physical properties as orthoclase and microcline. The MICAS are flaky and reflect light like minute pieces of tinfoil; muscovite is white, and biotite is amber-colored to black. CHLORITE resembles mica but is less lustrous and is dark green.
Some minerals of igneous rocks do not appear in pegmatites. Among them is OLIVINE, which has almost the same color as chlorite but is harder than a knife and is massive or granular. It is commonly associated with massive green SERPENTINE, which is softer than a knife. These three minerals are especially abundant in rocks found in the vicinity of Blandford, Massachusetts, and Dover and Chester, Vermont.
AUGITE is a dark brown to black pyroxene which occurs between the mosaic of whitish labradorite feldspar prisms in the weathered diabase near the Mount Holyoke House.
AMPHIBOLE crystals are dark green to black, “match-shaped” crystals. They have almost the same hardness as a knife and are characterized by two cleavages parallel to their length and intersecting at 56°. The mineral is also abundant in metamorphic rocks and is frequently reported as a “fossil fern” from ledges at Charlemont and Shelburne Falls.
The principal minerals of metamorphic rocks include many which are likewise present in pegmatites and igneous rocks, such as microcline, albite, quartz, muscovite, biotite, amphibole, serpentine and tourmaline. But there are others which are more exclusively metamorphic:
GARNET occurs in twelve- or twenty-four-sided red crystals. It is much harder than a knife. The geometric form is diagnostic, and crystals up to an inch thick are obtainable in Plainfield, Massachusetts, and at Grafton, Chester, and Gassetts in Vermont. They occur in a muscovite schist, in which the muscovite flakes are wrapped around the individual crystals.
TALC is a white to pale-green mineral found around the margins of intrusive rocks that are rich in olivine and serpentine. It is foliated and is so soft that even solid masses will rub off on cloth. It is present in the green marble quarry near Westfield.
KYANITE is a sky-blue, bladed mineral, with two excellent cleavages at nearly 90°, and a good smooth fracture at almost 90° to both. One face is harder than a knife and the other two are softer. It is very abundant in the country rock southeast of the Westfield marble quarry.
Aluminous minerals decay to KAOLINITE, and those with a high iron content alter to LIMONITE. Both these products of decomposition form a sticky paste in their original forms. Kaolinite is white to yellow, and limonite or ochre is yellow to orange. Limonite also appears in orange-colored or brown balls, in icicle-like masses, and in thin beds. Specimens have approximately the hardness of a knife. Quartz does not decay easily and remains behind in solid granules.
Most sedimentary rocks are formed by the cementation of deposits of transported waste, derived from older materials. They may contain anything. The minerals which undergo rapid decay break down to limonite, kaolinite and quartz, leaving only the more resistant varieties, which include, in order of decreasing resistance, quartz, microcline, orthoclase, albite and muscovite. Less abundant constituents are garnet, tourmaline, zircon and magnetite.
Certain kinds of sedimentary rocks may be formed through other agencies—for example, limestone, which is composed of calcite, initially precipitated by lime-secreting organisms or by the evaporation of lime-charged waters. The effects of organic activity may be seen in the limestone near Bernardston, but most of the calcite now present in the rocks of western Massachusetts is of vein or metamorphic derivation. Salt (halite) and gypsum are formed by the evaporation of saline waters, but only the vacated casts of salt crystals have been detected in the Triassic sediments of the valley.
Rocks record three distinct methods which nature employs in the aggregation of minerals. The sedimentary rocks register the work of wind, water and ice. Deposits left by wind and water are generally stratified or bedded, and they, together with glacial deposits, are composed of fragments which touch one another and are cemented at the points of contact. Igneous rocks record the solidification of hot liquids which injected themselves into older rocks or filled crevices, and which, upon cooling, formed masses of closely fitting crystals. The third group includes types which are crystalline like the igneous rocks, and which may be laminated somewhat like the sediments; they show effects of heating and squeezing until their original forms and even their minerals were changed. These are the metamorphic rocks.
Anyone who wants an orderly record of geologic history will arrange his rocks into these three groups—the sedimentary, the igneous, and the metamorphic. In the Connecticut Valley the metamorphic rocks reveal the ancient phases of earth history, and the sediments contain the details of younger or later geological episodes. The igneous rocks have a wider historical range; and, like the other types, they record a long period of violence and upheaval which seems out of harmony with the placid countryside for which they now provide a solid foundation.
The sedimentary rocks are built from the disintegrated wreckage of older ones. The products of rock decay are picked up and dragged, or carried in suspension or solution, by wind, running water, or moving ice. They are deposited when and where the transporting agent can no longer function. Such rocks are usually layered because the transporting power of the carrying agent fluctuates. Bands of one kind of material, separated by dissimilar materials above and below, are called beds.
The bedded or stratified rocks of the Connecticut Valley vary greatly, from the coarse bouldery deposits in Mount Toby to the fine-textured, red and black laminated beds at Whittemore’s Ferry. Conglomerate, arkose, graywacke, shale and even limestone are represented, but there is little true sandstone. Sandstone is an even-textured, granular rock, most commonly composed of cemented quartz grains. Its uniformity of grain-size and composition reflects prolonged weathering of the original rock and good sorting of the fragments as they were transported to their new resting place. The sequence of exposure, transportation and deposition was too rapid in the ancient Connecticut Valley to permit appreciable decay and sorting; hence sandstones are absent. Limestones and salt beds are likewise rare, but the metamorphosed limestones which are found in the western highlands and in the Berkshire valley demonstrate that limestone-forming processes played a significant, if intermittent, part in the history of the region.
CONGLOMERATE is consolidated gravel. Pebbles and boulders of all sizes are packed together by the stream which was moving them, and the spaces between the larger fragments are filled with the sand that settled in from the stream bed. The entire mass is cemented by silica, limonite, carbonates or some other substance deposited by percolating ground-water. The Devil’s football near the Mount Holyoke House is a famous piece which was dislodged from the hillside above; and excellent specimens may be collected on Mount Toby, on Mount Sugarloaf, and in the cut at Mount Tom Junction.
ARKOSE resembles conglomerate, but the individual grains consist of mineral fragments, among which reddish feldspar is prominent. Quartz and mica may be present, too; and all the pieces are characteristically angular, commonly ranging from ¹/₁₆ to ⅛ inch in size. The rock is red and crumbles easily. Beds of arkose alternate with conglomerate on the steep sides of Mount Sugarloaf.
GRAYWACKE is light to dark gray in color, and the fragments composing it are sand size pieces of older rocks. A few mineral grains, such as quartz, may be present, but mica is rare. Graywacke occurs interbedded with arkose in some parts of the valley.
SHALE is a thinly laminated sediment composed of microscopic quartz, feldspar, mica and kaolinite grains. Most shales in the Connecticut valley were deposited as muds in old lake beds. Some are red and record ephemeral pools, but others show from their black color, their coal layers, and their fish skeletons, that the water bodies in which they accumulated remained in existence for a comparatively long time.
LIMESTONE is a rock composed of calcium carbonate, and it consists essentially of an aggregate of calcite crystals or calcite fragments. It will give off gas bubbles in a very dilute solution of hydrochloric acid, and it exhibits other properties peculiar to the mineral calcite. A thin, sandy limestone bed has been identified in several sections of Holyoke.
Igneous rocks were once molten, and in this hot fluid state some were extruded at the surface as lava flows. Congealed flows reveal the motion, which brought them to their present resting places, in the banding and streaks that are so evident in the patterns of steam holes and minerals; but their massive structure bears witness to stagnation as they hardened. Other molten masses insinuated themselves into underground openings, where they solidified as intrusives, varying in size from small dikes less than an inch wide, to huge masses that can be measured in miles in any direction. Most of the igneous rocks in the highlands of western and central Massachusetts are massive intrusive types; light-colored varieties predominate, but some dark-colored dikes cut the older rocks both east and west of the valley. Dark-colored, massive and banded lavas are conspicuous in the ranges within the valley.
Igneous rocks may be divided into three general groups for practical classification, and each major group may be further subdivided. Rather conveniently each of the major groups may be recognized by the prevalent color of its rocks—whether dark, medium-colored, or light. And within each major classification there may be flows, characterized by banded structures and fine textures; small intrusives composed of well formed crystals in a fine-grained groundmass; and large intrusives consisting of goodsized, equi-granular crystals. Not all of these types can be found in central Massachusetts, but the variety of igneous rocks is surprising and offers some excellent possibilities for the collector.
The dark rocks owe their color to iron-bearing minerals like olivine, pyroxene (augite), amphibole and biotite. All of these minerals weather to a rusty red surface, which is typical of their outcrops at many places.
BASALT is a black rock, dense in some places but perforated with bubble holes or vesicles, at others. It occurs throughout the length of the Holyoke, Tom and Pocumtuck Ranges; and fragments of basalt are abundant in the Granby tuff and agglomerate.
DIABASE resembles basalt but is distinguished by the thin, short crystals embedded in it. These crystals of labradorite feldspar resemble pieces of clipped thread, and they sparkle in reflected light. Almost all dark-colored dikes and the slowly cooled central portions of thick lava flows consist of diabase.
PERIDOTITE is a dark green, coarse, granular rock composed of olivine and subordinate amounts of pyroxene. It occurs near Westfield and Blandford, and at many places in Vermont.
The medium-colored rocks contain approximately the same proportions of light- and dark-colored minerals. The dark iron-bearing minerals are relatively stable, but the light-gray feldspars decompose to kaolin and give the weathered rock a chalky white surface. Surface flows of this group are unknown in central Massachusetts, but the coarsely granular intrusives are well represented.
GRANODIORITE PORPHYRY is a greenish-gray rock occurring in many dikes in the western highlands. It has rectangular crystals of andesine feldspar up to ⅛ inch across, and these have a dull porcellaneous luster. A few dark-green amphibole crystals are only slightly smaller. Both feldspars and amphiboles are embedded in a very fine-textured, pale greenish groundmass.
GRANODIORITE is a gray equigranular rock containing flesh-colored microcline feldspar, white andesine feldspar, greenish flakes of chlorite, needles of amphibole and sparse grains of brown biotite. All crystals are about ¹/₃₂ inch thick and commonly display a parallel arrangement. This rock forms huge irregular masses at Williamsburg, Whately and Belchertown.
The light-colored rocks are well represented by dikes and large masses but not by recognizable surface flows in central Massachusetts. Their exposures have rarely weathered much, because the predominant minerals are quartz, microcline, orthoclase and albite, which resist decay.
QUARTZ PORPHYRY is a light gray rock that is found in dikes. It has porcelain-white cleavable feldspars up to ⅛ inch thick, and dark glassy quartz of equal size in a granular mass of very fine-grained crystals. Intrusives of this type are numerous in the vicinity of Whately.
GRAY ALBITE GRANITE occurs in many dikes and small irregular masses throughout the highlands. All crystals have approximately the same size and rarely exceed ¹/₃₂ inch in thickness. They consist of white orthoclase and albite, dark sugary quartz, and brown to black biotite.
RED MICROCLINE GRANITE is found in very large, irregular intrusives in the highlands. The crystals are ¹/₁₆ inch or more in thickness. The red color is due to the flesh-colored microcline. Quartz is dark and glassy, and muscovite is the typical mica.
Metamorphic rocks were once sedimentary or igneous rocks which have been changed by intense pressure, by heat, or by solutions moving through them. Pressure usually produces a sheeted or foliated structure along which the rock exhibits a tendency to part—somewhat like the pages in a book that was bound before the ink was dry. Percolating solutions may produce chemical alterations in the original materials and even crystallize new substances along the foliated surfaces within the rock, much as water circulating through cooled soil may solidify to ice and cause heaving. Many of the rocks in the highlands bordering the Connecticut Valley are highly foliated or banded in consequence of the mechanical deformation they suffered when the ancient upland mountain system was created. They include the slates, schists and gneisses. A few massive types, like marble, serpentine and soapstone, owe their origins chiefly to the effects of heat or of the hot, chemically charged solutions which permeated them.
SLATES are fine-grained rocks characterized by flat, parallel cleavage surfaces which usually cross the original sedimentary structure. They were formed from shales, by shearing and compression during ancient mountain-making movements. Slates crop out beside the station platform at Brattleboro, Vermont, and at many places southward along Federal Highway 5 to Greenfield.
SCHIST is foliated, too, but it is composed largely of cleavable minerals, such as chlorite, muscovite, biotite and amphibole, which are distributed along the cleavage surfaces. These minerals result from the chemical activity of hot solutions circulating along a slaty cleavage, re-crystallizing old materials, and bringing in new to make these coarse mineral flakes. The schist receives its specific name (biotite schist, chlorite schist, etc.) from the mineral which accentuates its cleavage structure.
A few schists contain large crystals which bulge the schistose surfaces outward around them. Garnet is characteristic in this role, and a muscovite schist with garnets in it is called a GARNETIFEROUS (or garnet-bearing) MUSCOVITE SCHIST. Other minerals with occurrences similar to the garnet are microcline, albite, staurolite, amphibole, tourmaline, pyrite and magnetite.
GNEISS is a banded rock containing cleavable minerals, but it lacks the cleavage structure of schist. The cleavable minerals (biotite, muscovite, amphibole, etc.) may give the gneiss its specific name, but as often as not, the name is derived from the whole mineral assemblage, or from an assumed origin, as in the case of granite gneiss. As in the igneous rocks, the mineral ensemble is held together by interlocked quartz and feldspar grains. Black-banded biotite gneiss and hornblende gneiss are the most abundant varieties in the neighborhood of the metropolitan reservoir east of Pelham.
MARBLE is a granular rock composed of calcite crystals. It is formed when heat volatilizes the bituminous coloring agents of ordinary limestone and simultaneously causes enlargement of the calcite grains. It is the principal rock in the Berkshire Valley in which North Adams, Adams and Pittsfield are located.
OPHICALCITE is a lime-silicate rock. It is formed by the chemical reactions of hot solutions on limestone or marble at considerable depth within the earth. The original calcite is converted into diopside, garnet, vesuvianite and tremolite, forming a rock that may be massive, or which may preserve some of the original bedded structure. It is found in association with the crystalline limestone and magnetite at the old iron mine, located one mile north of Bernardston.
SERPENTINE is a dark-green rock made almost exclusively of the mineral serpentine. It results from the reaction of hot solutions on olivine and pyroxene rocks (peridotites). Serpentinite is present in the Westfield marble quarry and at Zoar on the south side of the Deerfield River.
SOAPSTONE is composed principally of talc. It, too, results from the chemical activity of hot solutions ascending through serpentine and causing the mineral transformation. Bodies of this material are associated with the serpentinite at Westfield and Zoar, and northward in sections of Vermont. It is mined for talc, but in colonial days it found many uses. The colonists used cross-cut saws to make blocks for foot warmers in their sleighs, to control the heat in the old wood-fired ovens and to make water pipes before iron and lead were available in adequate quantities. Many soapstone articles may be seen—and purchased—in Wiggins Country Store and in other good antique shops through the valley. One of the most primitive Indian cultures in this region utilized soapstone pots, and exhibits are on display at both the Springfield Museum of Natural History and the Amherst College Museum.