That the sounds produced during earthquakes are carried through the ground faster than through the air appears clear from the fact that such sounds are sometimes heard in deep mines when they are not at all heard on the earth's surface.

In describing the earthquake that occurred in Kamtschatka, in 1759, Krashenikoff of St. Petersburg states that noises were heard like the rushing of a strong underground wind, accompanied by a hissing sound, which resembled the sizzlings heard when red hot coals are thrown in water.

In an earthquake that occurred in Lincolnshire, England, February 6th, 1817, a noise was heard closely resembling the sounds of wagons running away on a road. So complete and convincing was the resemblance that several wagoners on one of the roads drew their teams to one side so as to permit the runaway to pass safely.

Another kind of noise heard during earthquakes is a loud hollow bellowing. Sometimes, however, the sounds are more musical in their nature, being not unlike those produced by a very large organ pipe. At other times they resemble the noises produced when steam is blown into cold water.

The following account of earthquake sounds is given by Daubeny, in his book on volcanoes. It appears that during March, 1822, the people living on the island of Melida, opposite Ragusa, in Dalmatia, were greatly alarmed by sounds that at first they believed due to cannonading either at sea or on the neighboring coast. They afterwards found that these sounds were due to something that was taking place under the ground. The noises continued at intervals until August 23d, 1823, when a great earthquake occurred, during which one of the highest mountains on the island was cleft or split in one place. The underground noises continued from time to time and so frightened the people that they were about to leave the island permanently and emigrate to the mainland of Dalmatia. They were dissuaded from doing so by the government, and while the noises continued at intervals it so happened that no damage came to them. It is said, however, that twenty years after an active volcano broke out on the island.

There are various causes that produce earthquake sounds. A very slight rubbing or grinding together of rock surfaces may produce fairly loud noises, the volume of the sound being increased by transmission through the rock masses that lie in the path of the waves. An example of such an increase in the loudness of sounds is seen in the case of several of the large blocks of stone used for some of the piers of Kingston Harbor, in Ireland. When these rocks are moved together by blows of the waves they produce loud and appalling sounds, as if the whole island were being washed away. The same rocks, however, when left high and dry on the falling of the tide, can be caused to rub together, when moved by the hand. Under these circumstances, they produce but feeble sounds that can only be heard in their immediate neighborhood.

No doubt, some find it difficult to understand how it is possible for comparatively feeble sound-waves to be strengthened by their passage through large masses of solids. This is important and should be made clear. As everyone well knows, the ticking of a watch can only be heard at a short distance when the watch is held in the hand, because the sound-waves cannot readily pass through the body of the person holding the watch to the earth, the materials of the body not being sufficiently elastic. If, however, the watch be placed on the bare surface of a large wooden table from which the tablecloth has been removed, so that the watch can come directly in contact with the wood, and nothing else is placed on the table but the watch, the sound-waves are transmitted to the mass of the table and its entire surface sends them out into the air. The ticking of the watch can then be heard distinctly in almost any part of a large room.

Mallet states that in nearly all great earthquakes sounds are heard before the principal shock, and in his description of the Calabrian earthquake Hamilton says:

According to Dolomieu, during the Lisbon earthquake, the shocks were preceded "by a loud subterranean noise like thunder, which was renewed for every shock.... This great shock," he says, referring to one of the great upward shocks, "occurred without the prelude of any slight shocks, without any notice whatever as suddenly as the blowing up of a mine.... Some, however, pretend that a muffled interior noise was heard almost at the same moment."

The noises do not generally continue long after the earthquake shocks. In some cases, however, a very loud noise is heard at intervals for a considerable length of time after the principal shock. This was the case at Quito and Ibarra, in which a great noise was heard for from eighteen to twenty minutes after the principal shock. In a similar manner during the earthquake of October, 1746, at Lima, and Callao, South America, peals of underground thunder were heard at Truxillo for fifteen minutes after the principal shock. In such cases it seems probable that the noises were not caused by the same impulses that caused the original shock, but by the forces that caused the subsequent shock.

Humboldt relates that in 1784 there were noises heard at Guanajuato, from the 9th to the 12th of February. They were not, however, followed by an earthquake.

Humboldt also states that in an earthquake which occurred on the 30th of April, 1812, on the banks of the Orinoco River, in South America, a loud thundering noise was heard, without, however, any shock, but at this time a volcano on the island of St. Vincent, in the Lesser Antilles, although some 632 miles to the northeast, was pouring out streams of lava. Again in the great eruption of Cotopaxi, in 1734, underground noises were heard as if cannon were being fired. These sounds were distinctly heard at as great a distance as Honda on the banks of the Magdalena River. Now, bearing in mind that the crater of Cotopaxi is situated on the high plateau of Quito, in a region full of valleys and fissures, it would seem that for the sounds to have been sent through the 436 miles between the mountains and the valley of the Magdalena River, the waves must, for the greater part, have been transmitted through the solid earth at some considerable distance below the surface.

Mallet states that the underground noises which continued for more than a month from the midnight of January 9th, 1784, at Guanajuato, were not followed by any earthquake shocks, that it was if as thunder clouds occupied the space below the surface at that part of the earth and from these clouds there came the slow rolling sounds like short, quick, snaps of thunder.

Major Dutton in his book entitled "Earthquakes in the Light of the New Seismology" gives the following as the principal signs that herald the coming earthquake in the open country.

There are many other curious phenomena besides earthquake sounds or noises. Among some of the more interesting are the fire and smoke that are seen to come out of fissures that have been rent in the ground.

It is possible that in many cases these flashes of fire are in reality produced by electric discharges that momentarily light the clouds of dust thrown up out of the fissure. But sometimes true flames are seen escaping from the fissures. This was the case during the earthquake of Lisbon, in 1755, when fire burst through fissures at several places, burning with a lambent flame for some hours.

The clouds of dust that follow the rending of mountain masses by earthquakes are probably to be traced to the fracture of the rock masses, the dust so formed being violently thrown forth by the air squeezed out of the fissures, when they are suddenly closed. The violent compression of this air may raise this dust to incandescence.

Mallet asserts that in many cases the clouds of smoke observed do not consist of true smoke like that produced when wood or vegetable matters are incompletely burned, but is only ordinary air mixed with sulphurous acid gas, and various other gases.

But not only fire and smoke are seen at times coming out of fissures in the earth. A thing still more frequently thrown out is water, which often spouts forth along with great quantities of mud, sand, and the finely ground fragments of earthy materials generally. Among many other instances where the emission of water from the crevices was particularly noticeable, may be mentioned the earthquakes at Jamaica in 1687 and 1692. Here the water, in some places, was thrown out of the ground to considerable heights in the air.

Mallet calls attention to the fact that the waters of springs collect in reservoirs consisting either of fissures or crevices of the rocks, of small width but great depth, which are vertical or inclined to the horizon, or in reservoirs that are formed of extended beds of sand or gravel.

Now, when the earthquake waves moving horizontally over the surface produce movements that squeeze these fissures together, the water in the fissures is spurted out in high jets, and carries with it the finely divided rock or sand formed by the rubbing together of the rock surfaces. In the case of the reservoirs consisting of beds of sand or gravel, lying between impervious layers, if, during an earthquake motion, the land areas are suddenly lowered, the water rushing into the cavity thus left will afterwards be shot out with considerable force, when the land is suddenly raised again.

Where there are no direct openings in the ground the water will burst through the crust in the shape of great vertical jets, thus forming a circular hole, broken or fractured at its edges. Water jets of this character were especially numerous during the earthquake of Calabria in 1783. In a swampy plain, known as Rosarno, many of these circular wells or openings about the size of an ordinary carriage wheel, though in some cases much larger, were to be seen crowded together. The appearance of the openings are represented in Fig. 40.

Some of these were filled with water, but the greater number were dry and filled with loose sand. These latter, when examined by digging, were shown to be funnel-shaped, as seen in Fig. 41. As seen, the margins of the wells exhibit a series of cracks or crevices extending radially outward from the centre. Their origin is evident. As the water was violently expelled by the squeezing motion of the upper and lower impervious strata, it shot upwards, thus producing the funnel-shaped tube. At the same time the force of the eruption was sufficiently great to produce the radial fissures or fractures at the sides.

But greater fissures than these have been formed by earthquakes, especially those of the class created by a slipping of the earth's strata. In the case of an earthquake on the South Island of New Zealand, in 1848, a fissure having an average width of eighteen inches could be clearly seen extending in a direction parallel to the mountain chain for a distance of sixty miles, and during a later earthquake in the same region, in 1855, a fracture was formed that could be clearly traced for a distance of nearly ninety miles.

In some cases these fissures or fractured parts of the crust are left with one of their sides at a higher level than the opposite side. This was the case of the great Japanese earthquake of October 28th, 1891.

There are three kinds of waves produced by earthquakes; namely, the earthquake waves proper through the earth; the sound waves in the air, and great forced waves in the sea.

The sound waves of course reach the air from the point of origin below the earth's surface through the solid materials of the crust, and take on the curious varieties already described in connection with the sounds accompanying earthquakes.

We have already briefly described the manner in which the earthquake waves travel through the materials of the earth's crust. There remain to be discussed the great waves that are rolled up in the ocean during an earthquake shock. These waves are, perhaps, among the most destructive phenomena of great earthquakes. The following are only some of the more remarkable of such waves, and have been taken from Mallet's collection of earthquake data.

During some of the great earthquakes on the coasts of Chile and Peru, huge waves from the ocean did great damage when they reached the land. In the earthquake of 1590, ocean waves rushed for several leagues inland over the coast of Chile, carrying with them ships that were left high and dry as the wave receded. In the earthquake of 1687, Callao was inundated by a great wave from the Pacific Ocean, and ships were carried a full league into the country. During the earthquake of 1746, Callao was again swept away by a huge ocean wave. At later times earthquake waves have caused great damage to several other parts of the coast of South America.

Ocean waves of this character are formed by successive upward and downward movements at the bottom of the ocean, following each other at very brief intervals. Le Conte points out that the sudden upheaval of the bed of the ocean forms a huge mound in the surface of the water which results in a large wave that spreads rapidly in all directions. Waves produced in this manner sometimes reach a height of fifty to sixty feet. They are not readily observed in the deep ocean, but as soon as they reach the shallow waters near the shore they rush forward, forming waves from fifty to sixty feet in height and, rushing over the land, sweep everything before them.

During the great Lisbon earthquake of 1755 a huge wave started at a point fifty miles off the coast of Portugal. Half an hour after the earthquake was over several waves, the largest of which was sixty feet in height, rushed over a part of the city and greatly increased the ruin already wrought by the earthquake. According to Le Conte the great waves so formed moved in all directions across the Atlantic Ocean. They were thirty feet high when they reached Cadiz, eighteen feet in height at Madeira, and five feet on the coast of Ireland. They even crossed the Atlantic, being observed on the coasts of the West Indies.

A great ocean wave accompanied the Japanese earthquake in 1854. As in the case of the Lisbon earthquake this wave started in the bed of the ocean off the coast of Japan and only reached the island half an hour afterwards. It was thirty feet in height, and completely swept away the town of Simoda.

Owing to water's greater freedom of motion earthquake waves travel greater distances through the water than they do on land.

Of course, great earthquake shocks as a rule cause a very large loss of life. The following figures from Mallet give some idea of the extent of this loss, which is generally a matter of a few moments.

In the Lisbon earthquake, where the worst shock lasted a few seconds, 60,000 people were killed. During other earthquakes the losses have been as follows: 10,000 at Morocco; 40,000 in Calabria; 50,000 in Syria, and probably 120,000 in earthquakes that occurred in Syria in a. d. 19 and in a. d. 526.

But even these figures give only a meagre idea of the vast loss of life that has occurred during the past. It is said that during the reign of Justinian, earthquakes repeatedly shook the whole Roman world. The city of Constantinople was visited by earthquake shocks that continued at intervals for forty days. Deep chasms were opened in the earth and huge masses were thrown into the air. Enormous sea-waves were formed. At Antioch, during the earthquake of May 20th, a. d. 526, 250,000 people are believed to have been killed.

On the 31st of July, a. d. 365, in the second year of Valentinian, a dreadful earthquake shook the Roman world, and a great wave rolled in from the Mediterranean and swept two miles inland, carrying ships over the tops of houses. During this earthquake 50,000 people lost their lives at Alexandria.

In the earthquake of Messina in 1692, 74,000 people are said to have been killed; and, according to other accounts, 100,000. In the year a. d. 602, another earthquake at Antioch killed 60,000 people.

During the earthquake of Quito, in 1797, Humboldt estimates that 40,000 natives were either buried in crevices in the earth, under the ruins of buildings, or were drowned in lakes and ponds that were temporarily formed.

In this connection Mallet writes as follows:

Necessarily the progress of a great earthquake wave will produce great changes in the earth's surface features; for example, landslides, where immense layers of clay or other material slip or slide to a lower level and are thrown across the course of a river, causing its waters to be dammed up and then by spreading to form great lakes.

Sometimes, after vast bodies of water have been collected in this manner, disastrous floods result later from a sudden giving way of the barrier, and the loss thus caused is occasionally far greater than that directly due to the earthquake.

Permanent changes of level are frequently caused by earthquakes, as, for example, the coast of Chile during the earthquake of November 19th, 1822, where the coast for many miles was raised from three to four feet above its former plane.

In other cases the level of the ground is permanently lowered. This occurred in the Bengal earthquake in 1762, when an area of some sixty square miles suddenly sank, leaving only the tops of the higher points above water.

In some cases of changes in the level of the ground, large areas being raised in one place and lowered in another, rivers take new courses, and their old courses are completely obliterated.

CHAPTER XXV

THE EARTHQUAKE OF CALABRIA IN 1783

All students of elementary geography are quick to notice that the extreme southeastern part of Italy is shaped something like a boot, which appears to be kicking at the island of Sicily. This part of the Mediterranean Sea has for very many years been the arena or storm centre of more or less intense volcanic activity. To the northwest is the active volcano of Vesuvius, as well as the volcanic regions of the Phlegræan Fields. Immediately opposite the point of Italy, near the toe of the foot, is the active volcanic mountain, Etna, while not far from this point is the volcano of Stromboli.

In 1783 this part of the world was visited by a very severe earthquake. Since at that time the country was divided into two parts, known as Upper Calabria and Lower Calabria, this earthquake is sometimes spoken of as the earthquake of the Calabrias, or more simply as the Calabrian earthquake.

The great mountain range of the Apennines, mainly of granite formation, extends through the central part of Italy. The lands adjoining the mountains on each side are flat and marshy, and consequently unhealthy.

Numerous observers have compiled excellent accounts of the Calabrian earthquake. These, having been made by educated persons, are, to a large extent free from the inconsistencies and exaggerations apt to characterize descriptions by ignorant persons, especially when in a condition of excitement or alarm. Among reliable writers was Sir William Hamilton, who made a personal examination of the region, soon after the first severe shock, and collected much valuable information for a paper which was afterwards published in the Philosophical Transactions of the Royal Society. Then, too, Dolomieu, another scientific man of high ability, made a careful study of the effects produced by the earthquake.

As can be seen by an examination of the map presented in Fig. 42, the part of Italy included in the Calabrias covers an area from north to south almost equal to two degrees of latitude. Although the shock extended beyond the limits of Calabria, since it reached as far north as Naples, as well as over a great part of the Island of Sicily, the territory in which the greatest damage was done did not exceed in area about 500 square miles.

The southern part of Italy is subject to frequent earthquake shocks. Pignatari, an Italian physician, asserts that this region was visited during 1783 by no less than 949 earthquakes, of which 501 were of the first class, or degree of intensity, while in 1784, there were 151 earthquakes, of which ninety-eight were of the first class.

It seems that the city of Oppido, marked on the above map as midway between the two coasts, was the point from which the severe earthquake of 1783 started. If one draws a circle, with a radius of twenty-two miles, around Oppido as a centre, the portions of the Calabrias that were the most affected will all lie within this circle.

The great Calabrian earthquake was attended by numerous shocks. The first and the most severe shock, that of February 5th, 1783, was only two minutes in destroying most of the houses in all cities, towns, and villages on the western side of the Apennines in this part of Italy.

Another severe shock occurred on the 28th of March. This shock was almost as severe as that of February 5th.

In order to understand many of the effects produced by this earthquake, inquiry must be made into the geological character of the region. According to Dolomieu, the flat country at the slopes of the Apennines, known as the Plain of Calabria, is covered with sand and clay mixed with sea shells. These strata have been deposited by the sea from materials that have been obtained by the decomposition of the granite mountain ranges in the Apennines. The plain is quite level except where it is crossed by deep valleys or ravines, which have been eroded or cut by the swift mountain torrents. In many cases, these ravines or valleys have depths as great as 600 feet. Their sides are generally almost perpendicular. Consequently, as Lyell remarks, throughout the length of the mountain chain, the soil, which adheres but loosely to the granite base of the mountain chain, could therefore be easily separated from the mountain, and sliding over the solid steeps of the mountain could readily move, especially through the ravines or gorges, to distances in some cases as great as from nine to ten miles.

This peculiarity of the country must be thoroughly understood, since, otherwise, it would seem impossible that lands could be carried several miles from their former position, and often bear along with them almost undisturbed houses, olive groves, vineyards, and cultivated fields.

The heaving of the surface of the earth like the waters of the sea, so common in severe earthquakes, occurred during the Calabrian earthquake. In some places this heaving so shook the trees that they bent until their tops touched the ground near their base.

Parts of the ground were violently thrown upwards into the air as in the explosive type of earthquakes. In many instances the large paving stones were thrown into the air and afterwards found with their lower portions upwards.

During the earthquake deep fissures were made in the earth at various localities and there were, moreover, marked changes of level. At Messina in Sicily the shore was fissured and rent and while before the convulsion the surface had been level, it was afterwards found to be inclined toward the sea.

According to Dolomieu the following curious incident occurred during the passage of the earthquake waves. A well in the ground of one of the convents of the Augustines, lined on the inside with stones, was so affected by the upward thrust given to the land that its stone lining was left projecting above the level of the earth in the form of a small tower some eight or nine feet in height.

Frequent instances occurred of deep fissures in the surface of the earth. Many of these remained open after the earthquake, although in other cases they were firmly closed together before the earthquake shocks ceased.

Fig. 43 represents the appearance of certain fissures in a part of Calabria during this earthquake. These cracks, it will be noticed, radiate or pass outward in all directions from a central point, just like the cracks that are formed in a glass window pane when it is fractured by a stone thrown against it.

Of course, the most violent effects were near the origin of the earthquake at Oppido. Here the formation of deep fissures was common. In another part of the country a number of buildings were suddenly swallowed up in a central chasm, which almost immediately closed, thus permanently burying all these objects.

Some idea of the force with which the fissures were afterwards closed can be formed by reflecting on a case where, in order to recover some of the buried articles, the ground was dug up at these points, and it was found that the materials, human bodies and other objects, were so jammed together as to make one compact mass.

To Sir William Hamilton a place was shown where the fissures, though, when he saw them, they were not more than a foot in width, had opened sufficiently wide during the shock to swallow up a hundred goats as well as an ox.

An earthquake that caused such marked changes in the appearance of the earth's surface, naturally made great changes in the direction of the rivers. In one case the end of a small valley was so completely filled with stones and dirt that the water was dammed up, producing a lake two miles in length and one mile in breadth. In a similar manner no less than 215 lakes were formed in different portions of Calabria.

Of course, in the flat country at the base of the Apennines, frequent landslides occurred, the land sliding into great chasms and continuing to move down them for considerable distances, so that in many places pieces of land containing olive trees, vineyards, and green fields, were bodily transported for distances of several miles. This, moreover, was done so quietly as to leave the houses entirely uninjured, and the trees and other vegetation continuing to grow up with apparently no marked decrease in vitality.

As is usual in such cases, the sudden and strong blows acting on the waters of the sea, killed great numbers of fish just as does the explosion of dynamite at a point below the surface of the water; and in a similar way the fish that usually live at the bottom of the sea in the soft mud, being disturbed by the earthquake shocks, came near the surface where they were caught in vast numbers.

It is an interesting fact that during this earthquake the volcano of Stromboli showed a marked decrease in the volume of smoke it gave out. Etna, however, was observed to emit large quantities of vapor during the convulsion.

Lyell tells the following story of the Prince of Scilla, who with many of his vassals sought safety in their fishing boats. Suddenly, on the night of February 5th, while some of the people were sleeping in the boat, and others were resting on a low plain near the sea, in the neighborhood, another shock occurred, a great mass was torn from a neighboring mountain and hurled with a crash on the plain, and immediately afterwards a wave, twenty feet or more in height, rolled over the level plain, sweeping away the people. It then retreated, but soon rushed back again, bringing with it many of the bodies of the people who had perished. At the same time all the boats were either sunk or dashed against the beach, and the Prince with 1,430 of his people was destroyed.

The total number of deaths caused by this earthquake in the Calabrias and Sicily were estimated by Hamilton at 40,000. Besides these about 20,000 more perished in epidemics that followed the earthquake, or died for lack of proper food.

CHAPTER XXVI

THE GREAT LISBON EARTHQUAKE OF 1755

Lisbon, the capital of Portugal, on the Tagus River, is built along both banks for five miles, and on several small neighboring hills. It is supplied with water by means of an aqueduct, called the Alcantara, which brings the water from springs about nine miles to the northwest. For portions of its length the aqueduct is placed underground, but where it crosses the deep valley of the Alcantara it is supported, for a distance of 2,400 feet, by a number of marble arches, which in one place are 260 feet in height. This fact is put forward not merely for the sake of its artistic interest, but because, strange to relate, this part of the aqueduct remained uninjured during that great earthquake, the greatest of modern times.

On the 1st of November, 1755, this frightful catastrophe, according to Lyell, from whose excellent account much of the information contained in this chapter has been obtained, struck the beautiful city almost without any warning. Terrible sounds came suddenly from underground; almost instantly afterward a violent shock threw down the greater portion of the city; in less than six minutes 60,000 people were killed.

The place from which this earthquake started must have been situated on the bed of the ocean at some distance from the coast; for the great wave thus raised in the Atlantic Ocean did not reach the mouth of the Tagus River until about half an hour after the most severe shocks were over. The arrival of this wave at the mouth of the Tagus was announced by the sea retiring to such an extent as to leave the bar dry. Then a huge wave, sixty feet in height, rolled in from the ocean and completed the work of destruction that had been commenced by the earthquake.

So great was the shock that the mountains in the neighborhood were violently shaken and some of them split or fractured in a most wonderful manner.

Particularly large was the loss of life in the churches whither hundreds hastened for refuge when the shakings of the earth began, for most of these buildings fell and buried the worshippers. Another immense loss of life was caused by the destruction of a large marble quay or wharf that was suddenly swallowed up by the sea. While the buildings in the city were being overthrown by the violent shakings of the earth, a multitude sought the quay as a flat place where they could not be injured by the falling buildings. Suddenly, however, this structure sank into the water and not only were all the people drowned, but none of the bodies was ever afterwards found.

Failure to find any remnants of the pier or any of the people who perished on it has been attributed to the formation of eddies or whirls that were sufficiently strong to carry down vessels by suction similar to that of the famous maelstrom off the coast of Norway. Of course, in a time of boundless excitement like that of the Lisbon earthquake, accounts are apt to be highly exaggerated. For example, assertions are made in many books that the water left in the harbor after the sinking of the quay was unfathomable. Now, in point of fact, the depth of this place has been measured and found to be less than 100 fathoms.

When it is remembered that not one of the bodies of the people on that quay was ever again seen, it is possible, as Lyell suggests, that a deep fissure or chasm opened immediately on the ground on which the quay stood, so that it, together with all on it, were dropped into the chasm, which, closing, buried them deep in the earth.

The Lisbon earthquake was especially noted for the extent of country affected by it. Humboldt estimated this area as being more than four times the size of Europe. In parts of this area immense mountain ranges, such as the Pyrenees, Alps, etc., were violently shaken. When the size of these mountains is considered one realizes that it must have required a mighty force to shake them. These shakings were so severe that they produced a deep fissure in the ground in France. Continuing towards the north the solid earth was shaken as far as the shores of the Baltic and Norway and Sweden, generally. This, of course, included the flat country of Northern Germany. The hot springs of Toplitz disappeared for a time, but, breaking out afterwards, discharged such quantities of muddy water that the surrounding country was inundated.

The waves crossed the Atlantic, causing high tides on the island of Antigua, Barbadoes, and Martinique, of the Lesser Antilles, where, instead of the usual tides of two feet, tides of twenty feet high were observed. Further to the north the waves reached the eastern shores of North America, and shook the continent as far west as the Great Lakes, and spread in the North Atlantic as far as Iceland.

Toward the south the waves affected parts of northwestern Africa, where much loss of life occurred in the villages some eight leagues distant from the city of Morocco. Here from 8,000 to 10,000 people were killed, being swallowed up by deep fissures in the earth, which afterwards closed on their bodies.

Severe shocks were in many cases felt on vessels at sea. In one instance, although the vessels were at considerable distances from where the waves started, the captains reported that the shocks were so great that on several occasions it was believed the vessel had struck a rock, till, on heaving the lead, they found that they were in very deep water. In another instance, such was the shock to the vessel that the planks on the deck had their seams opened. In still another case several of the sailors were thrown into the air for a distance of about one and a half feet.

It has been frequently observed that when great earthquakes happen, curious changes take place in the level of the waters of lakes entirely disconnected with the ocean; for example, mountain lakes, far above the level of the sea, the water suddenly rising and then resuming its original level. Sometimes the waters of such lakes have suddenly disappeared, probably being drained off through a fissure formed in the bed of the lake. In such event the lake generally remains dry after the passage of the earthquake.

At the time of the Lisbon earthquake it was observed that the water of Loch Lomond in Scotland first rose above its ordinary, then sank again to its usual level. This difference of level is explained by Lyell as follows: when the earthquake waves reached the lake, the water being unable to take the sudden shove given to it by the earthquake waves, dashed over that side of the basin which first received the shock. Assuming this to be the case, since the rise of the level in the water of Loch Lomond was two feet and four inches, it is comparatively easy to calculate the speed of movement that the earthquake waves had, when they reached this body of water. Calculated in this way it would seem that the waves had a speed of about twenty miles a minute.

But what especially characterized the Lisbon earthquake were the great waves that were produced in the ocean. Besides the huge wave that entered the Tagus, a wave of the same height swept eastward along the southern coast of Spain, and the northwestern coast of Africa. At Tangier in Africa it swept the coast as a very high wave no less than eighteen times, or, in other words, eighteen huge waves rolled in from the ocean. At Funchal, on the Madeira Islands, this wave rose fifteen feet above the high water mark.

Many attempts have been made to explain the manner in which the great sea waves are started in earthquake movements. Some believe that they are due to the sudden raising or heaving up of the water, far above ordinary level. But, as Lyell points out, this explanation would not be satisfactory for the waves produced in the case of the Lisbon earthquake, since it would fail to account for the fact that both on the coasts of Portugal as well as on the island of Madeira the high wave was preceded by a movement of the water toward the point of origin; that is, the waters moved away from Lisbon and the Madeira Islands, so as to leave the water very low at those points, when shortly afterwards a huge wave rushed in from the sea and swept over the land.

Earthquake waves move much more rapidly through the solid rocks of the earth's crust than through the waters of the ocean. The shock transmitted through the solid earth from Lisbon to the Madeira Islands took only twenty-five minutes to reach the islands, while the waves in the ocean took about two and a half hours to cover the same distance.

CHAPTER XXVII

THE EARTHQUAKE OF CUTCH, INDIA, IN 1819

Cutch is one of the Provinces of India lying on the western coast of Hindostan, east of the delta of the Indus River.

A great earthquake occurred in this region on June 16th, 1819. As indicated by the map presented in Fig. 44, by Lyell, the district of Cutch lies on the coast of the Arabian Sea. Cutch is at times a peninsula, being washed on the south and east by the Arabian Sea and the Gulf of Cutch, and on the north by a depression known as the Runn of Cutch which, during unusual tides, is overflowed by the waters of the sea, but for the rest of the year is dry.

The earthquake of Cutch was apparently central at the town of Bhooj, where the destruction was extreme, hardly a house being left standing. The shock extended over a radius of about 1,000 miles from Bhooj, reaching to Khatmandoo, Calcutta, and Pondicherry.

At Anjar the fort, together with its tower and guns, were completely ruined. The shocks continued at intervals after the principal shock until June 20th, when the volcano of Denodur is said by some to have emitted flames, although this is denied by others.

Great changes were produced in the eastern channel of the Indus, which forms the western boundary of the Province of Cutch. The water in this inlet had become so low that it was readily fordable at low tide at Luckput, and was only covered with six feet of water at high tide. After the earthquake it deepened at the port of Luckput to over eighteen feet at low tide, while in other parts of the channel the water had deepened from four to ten feet at high tide, where before the earthquake shock it had never been deeper than from one to two feet. Indeed, after these changes the inland navigation of the country again became possible after having been closed for many centuries.

The Cutch earthquake resulted in a marked depression of the country, especially north of Luckput, where the fort and village of Sindree were so quietly sunk that the fort, with its tower and walls, was left projecting slightly above a body of water that not only completely covered the old site but also formed a large lake marked on the preceding map, at Sindree, by the dark shading. It was this change of level that deepened the eastern channel of the Indus, just mentioned.