134 



IGNEOUS AGENCIES. 



and making history is far greater than that of all other igneous agen- 

 cies put together. It is probable that the same causes which are now 

 at work gradually raising or depressing the earth's crust have during 

 geological times formed the continents and the seas. 



Elevation or Depression during Earthquakes.— We have already 

 spoken (page 105) of sudden elevations or depressions of great areas 

 of country at the time of earthquake-occurrence in Hindostan, in the 

 valley of the Mississippi River, and especially of the southern part of 

 South America. It is not probable, however, that much is accomplished 

 in this paroxysmal way. These cases are referred to in order to show 

 the close connection of such sudden bodily movements, and therefore 

 presumably, also, of the slower movements about to be described^ with 

 the causes and forces which produce earthquakes. 



Movements not connected with Earthquakes— South America.— Be- 

 sides the sudden elevation of Chili and Patagonia by earthquakes, the 

 same countries show evidences of gradual elevation on a stupendous 

 scale. The evidences are old sea-beaches, full of shells of species now 

 living in the adjacent sea, far above the present water-level. These 

 " raised beaches " have been traced 1,180 miles on the eastern shore 

 and 2,075 miles on the western, and at different levels from 100 to 1,300 

 feet above the sea. More recently Alexander Agassiz has traced them 

 by means of corals still sticking to the rocks to the height of nearly 

 3,000 feet.* It is not probable that all this movement took place dur- 

 ing the present geological epoch, but it is the more instructive on that 

 very account, since it shows the identity of geological causes with causes 

 now in operation. 



Italy. — The most carefully-observed instance of gradual depression 

 and elevation is that of the coast of Naples. Fig. Ill is a map and 

 Fig. 112 a section of the coast of the bay of Baise, near Naples. ' Be- 



FlG. 111. 



Proceedings of the American Acidemy of Sciences, vol. xi, p. 287, 1S76. 



