398 



GEOLOUV. 



district of Plaisano, a rent, of nearly n mile in length, 

 one hundred and five feet broad, and thirty feet deep 

 opened ; and in the same district two gulfs arose, one 

 at Cerzulli, three quarters of a mile long, one hundred 

 and fifty feet broad, and about one hundred feet 

 deep ; and another, nearly a quarter of a mile long, 

 about thirty feet broad, and two hundred and twenty- 

 five feet deep. Ulloa relates that in the earthquake 

 of 1746, in Peru, a rent took place, which was two 

 miles and a half long, and four or five feet wide. 

 These rents sometimes close again ; thus, in the year 

 1<>92, in the island of Jamaica, during an earth, 

 quake, the ground heaved like a boiling sea, and 

 was traversed by numerous rents, two or three hun- 

 dred of which were often seen at a time opening and 

 closing rapidly again. 



It is evident that if the land is fractured and then 

 traversed with vast rents, by earthquakes, tliat por- 

 tion of the land will in some places sink and in 

 others rise, and this not once but several times in 

 the same place. In the year 1772, during an erup- 

 tion of one of the loftiest mountains in Java, the 

 ground began to sink, and a great part of the vol- 

 cano, and part of the neighbouring country, estimated 

 to be fifteen miles long and six miles broad, was 

 swallowed up. During the earthquake at Lisbon in 

 1755, a new quay entirely disappeared ; thousands 

 of the inhabitants had taken shelter on it, to be out 

 of the reach of the tottering and falling buildings, 

 when suddenly the quay sunk down with its thou- 

 sands of human beings, and not one of their dead 

 bodies ever floated to the surface. In the year 1692, 

 during an earthquake in Jamaica, a tract of land 

 about a thousand acres in extent sank down in less 

 than a minute, and the sea immediately took its place. 

 On the north side of the island several large tracts 

 with their whole population were swallowed up, and 

 a lake appeared in their place covering above a 

 thousand acres. Numerous examples of the uprais- 

 ing of the land by earthquakes might be given ; we 

 shall enumerate a few of them. On the 19th No- 

 vember, 1822, a most dreadful earthquake visited 

 the coast of Chili ; the shock was felt at the same 

 time throughout a space of one thousand two hundred 

 miles from north to south. When the country around 

 Valparaiso was examined on the morning after the 

 shock, it was found that the entire line or coast, for 

 the distance of more than a hundred miles, was raised 

 above its former level. The area over which this 

 upraising took place was estimated at one hundred 

 thousand square miles : the rise upon the coast was 

 from two to four feet ; at the distance of a mile in- 

 land, it was estimated from five to seven feet. On 

 the 18th of March in the year 1790, at St Maria di 

 Niscomi, some miles from Terranuovo, near the south 

 coast of Sicily, a loud subterranean noise was heard 

 under the town just mentioned, and the day after 

 earthquakes were felt ; then the ground gradually 

 sunk down for a circumference of three Italian miles, 

 during seven shocks, and in one place to a depth of 

 thirty feet ; as the subsidence was unequal, rents 

 were formed, some of which were so wide that they 

 could not be leaped over : this gradual sinking con- 

 tinued to the end of the month. About the middle 

 of this period an opening took place in the subsiding 

 land, about three feet in diameter; through which 

 continued to flow, for three hours, a stream of mud, 

 which covered a space sixty feet long and thirty feet 

 broad ; the mud was saltish and composed of chalky 

 marl and a viscid clay, with fragments of crystalline 

 limestone ; it smelt of sulphur and petroleum. On 

 the 16th June, 1819, at Cutch in Bombay, a violent 

 earthquake took place, during which, independent 

 of other changes, the eastern and almost abandoned 

 channel of the Indus was much altered : this estuary 



was, before the earthquake, fordable at Luckput, 

 being only a foot deep when the tide was at ebb, and 

 at flood tide never more than six feet ; but it was 

 deepened at the fort of Luckput, after the earthquake, 

 to more than eighteen feet at low water, showing that 

 a considerable depression had taken place. The 

 channel of the river Runn was so much sunk that, 

 instead of being dry as before, during that period of 

 the year, it was no longer fordable except at one 

 place ; and it is remarked by Captain Macmurdoch, 

 and the observation is of high geological import, 

 as connected with the formation of valleys, of river 

 districts, &c. " should the water continue through- 

 out the year, we may perhaps see an inland naviga- 

 tion along the northern shore of Cutch; which, from 

 stone anchors, &c., still to be seen, and the tradition 

 of the country, I believe to have existed at some for- 

 mer period." Sindree, a small mud fort and village 

 belonging to the Cutch government, situated where 

 the Runn joins the Indus, was overflowed at the time 

 of the shock. The people escaped with difficulty, 

 and the tops of the houses and walls are now alone 

 seen above water. In the year 1790, in the Carac- 

 cas, during an earthquake, a portion of granite soil 

 sunk, and left a lake 800 yards in diameter, and from 

 eighty to an hundred feet deep : it was a part of the 

 forest of Aripao which sunk, and the trees remained 

 green for several months under water. 



For a further account of the general relations of 

 the earth, and of its surface, we refer to the articles 

 Earth, Mountains, Sea, Air, Rivers, Glaciers, Atmo- 

 sphere, Earthquakes, J'olcanoes, &c. 



We shall now proceed to some more particular re- 

 marks on the component parts of the earth's crust, 

 or covering. This consists chiefly of various kinds 

 of rock and mountain masses, more or less extensive. 

 Rocks may be divided into homogeneous, apparently 

 homogeneous, heterogeneous or compound frag- 

 ments, loose mountain rocks, and coal strata. Ho- 

 mogeneous rocks, as quartz, limestone, gypsum, &c., 

 belong to the simple mineral species. In the appar- 

 ently homogeneous rocks, several species are united 

 in such minute particles, and with so ultimate a con- 

 nexion, that the parts cannot be distinguished by the 

 eye ; as in the case of basalt, &c. In the hetero- 

 geneous rocks, the component parts are more or less 

 easily distinguished, according to circumstances ; as, 

 for example, the quartz, feldspar, and mica, in granite. 

 Rocks consisting of confused fragments, as pudding- 

 stone, breccia, &c., are made up of variously formed 

 and mingled pieces of stones, held together by means 

 of a uniform paste, like themselves in hardness, but 

 generally of a different composition. Loose stones 

 and fine gravel, sand and loam, are all produced by 

 the mechanical division of large masses, by their 

 decomposition or disintegration from the action ot 

 air, moisture, &c., or from the continued action of 

 streams of water, torrents, &c. A particular place 

 in the mineral kingdom belongs to the species of 

 minerals produced by the destruction of some portion 

 of the vegetable world, constituting the various spe- 

 cies of coal. In regard to structure, rocks are crys- 

 talline, granular, slaty, compact, porphyritic, and 

 amygdaloidal. The crystalline granular rocks con- 

 sist of small crystalline or angular parts, fixed 

 together by the process of common crystallization. 

 In slaty rocks, the mass splits into thin plates or 

 layers. Rocks are called compact, of which all the 

 particles wear a uniform appearance, and which 

 assume no particular forms. Porphyritic rocks pre- 

 sent a compact and homogeneous basis, in which are 

 imbedded other minerals, in the form of insulated 

 crystals or grains. Some rocks contain roundish or 

 irregular cavities, which are either empty, or in part 

 or wholly filled with mineral substances of a different 





