UPHEAVAL AND SUBSIDENCE, 



xt/ c _. 181); sometimes one of the parts is elevated much higher 

 than the other (Jigs. 182, 183), showing that one must have been 

 raised while the other was sunk. 



Fig. 181. Fig. 182. Fig. 183. 



Changes of level produced by earthquakes. 



Again it happens that a more or less considerable extent of surface ia 

 suddenly sunk, carrying down plantations and habitations, leaving- yawning 

 chasms, with vertical sides, eighty or a hundred yards in depth. In certain 

 cases an immense quantity of water springs from the bottom of these cavi- 

 Jies, forming more or less extensive lakes, sometimes without apparent cur- 

 rent, and sometimes giving origin to impetuous torrents. In some instances, 

 on the contrary, rivulets were absorbed by the fissures in the earth, or swal- 

 lowed for a time, or forever. 



But, besides the numerous cracks and divers chasms which intercept the 

 waters, furnishing new springs, and giving them a new channel, it also 

 happens that masses of rocks, falling across valleys, arrest the waters and 

 soon form lakes in the upper part. Now, these accumulated waters make 

 new passages, either by breaking through the sides of the valley, or by en- 

 larging some fissure in the mountain ; or, they degrade, cut down, the obsta- 

 cle which retained them, and soon overturn it entirely or in part. Hence 

 arise those fearful outbreaks, those impetuous torrents rolling down enor- 

 mous masses of rock, the ravages of which are as disastrous as the earth- 

 quake itself, and which, excavating new channels, or widening and deep- 

 ening those that waters before pursued, mark their course by the debris 

 which they roll down and successively deposit. 



When the principal effects of earthquakes took place on the continent 

 between Oppido and Soriano, the phenomena extended as far as Messina, 

 across the straits ; more than half the city was destroyed, and twenty-nine 

 hamlets or villages were swallowed up. The bottom of the sea was sunk, 

 and disturbed at various points ; the shore was rent, and the whole ground 

 along the port of Messina was inclined towards the sea, suddenly sinking 

 several yards ; the whole promontory which formed its entrance was swal- 

 lowed in a moment. 



5. Upheaval and Subsidence. The earthquakes which occurred 

 on the coast of Chile in 1822, 1835, and 1837, have produced 

 effects not less remarkable. Different parts of the coast, from 

 Valdivia to Valparaiso, that is, an extent of more than two hundred 

 leagues, were evidently elevated above the waters, as well as many 

 neighbouring islands as Air as those of Juan Fernandez ; the bot- 

 tom of the sea to a considerable extent participated in this phe- 

 nomena. On the coast, rocks which had been previously under 

 water were raised two or three yards above its level, with the mol- 



5. Give some examples of upheaval and subsidence produced by earth- 

 quakes. 



