1886.] NEW YORK ACADEMY OF SCIENCES. 37 



earthquakes : — to those of 1602 and 1791, central in the St. 

 Lawrence valley, in the first of which the shocks continued for 

 months over an area of three hundred leagues; and to a number 

 of those on the west coast of South America so destructive in 

 Peru and Chili, and frequently accompanied by volcanic 

 activity, at points both near and remote in the Andean chain. 



The earthquake of 1811, known as that of New Madrid, was 

 most violent in the Mississippi valley. It was followed by shocks 

 at short intervals until March, 1812, when one of great severity 

 destroyed the city of Caraccas, in Venezuela. 



Accepting the nebular hypothesis, the evidence points to an 

 earth crust from twenty to fifty miles thick, resting upon the 

 plastic, semifluid contents of the interior. Volcanoes are the vents 

 of this interior. Where earthquakes occur in the volcanic regions 

 of Southern Italy, of Java, of the Moluccas, and of the region of 

 the Andes, as the greater number do, they seem to have an intimate 

 association with the volcanoes. The quantities of matter sud- 

 denly ejected from these volcanoes, attended by explosions and 

 the conversion of masses of water into superheated steam, must 

 create cavities of the fluid contents, into which the flexible crust 

 settles by gravity or pressure, causing surface elevations and de- 

 pressions. Mere shrinking by cooling woul4 not produce rugged 

 mountain chains of their present form. Combined with these 

 dynamic forces, more active in earlier cosmic ages, they were 

 quite adequate to elevate the Andes or the Himalayas. All the 

 phenomena of earthquakes in volcanic regions indicate their 

 deep-seated origin and their connection with disturbances of the 

 fluid interior of the earth. 



There was another group of earthquakes which occurred in 

 regions of slight or no volcanic activity, some of them too re- 

 mote from volcanoes to have any connection with them. If at- 

 tended by volcanic eruptions, these never preceded, and always 

 ceased with the convulsions. Yet they were gigantic in their 

 phenomena — terrible in their devastating effects. What and 

 whence was their origin? Were they due to the expansive force 

 of vapors in subterranean cavities; to a slipping of sections of 

 the earth crust upon each other; or to forces within the crust 

 itself, and not more than 10,000 or 20,000 feet from its exterior 

 surface? 



