168 REACTION OF THE INTERIOR OF THE EARTH 



more than 30,000 human beings lost their lives in 

 the course of a few minutes, ( 232 ) we still saw the once- 

 moving cones of Moya ( 233 ) which had been then pro- 

 truded from the ground, and the combustible substance 

 of which they consisted employed in the huts of 

 the Indians for cooking. I could describe changes 

 of surface resulting from that catastrophe, quite analo- 

 gous, on a larger scale, to those presented by the cele- 

 brated Calabrian earthquake (February 1783), and the 

 accounts of which were long declared to be incorrect and 

 exaggerated, because not explicable by too hastily formed 

 theories. 



Since, as I have already said, the considerations re- 

 specting the cause of the impulse to motion ought to be 

 carefully separated from those which relate to the nature 

 and the propagation of the waves of motion, the subject 

 is thereby divided into two classes of problems of very 

 unequal accessibility. In the first, as in so many cases 

 where we desire to ascend to the higher links in the chain 

 of causation, we cannot, in the present state of our 

 knowledge, look for any generally satisfactory results. 

 Nevertheless, while our efforts are directed to the dis- 

 covery of laws in phenomena which we are unable to 

 make the subject of actual observation, great cosmical 

 interest attaches to our at the same time keeping con- 

 stantly in view the different modes of genetic explanation 

 which have been put forward as probable. The greater 

 part of these (as in regard to all volcanic action or 

 volcanicity) relate, under various modifications, to the 

 high temperature and to the chemical constitution of 

 the molten interior of the earth ; one other most recently 

 proposed mode of explanation of earthquakes in trachytic 



