ON ITS EXTERIOR. EARTHQUAKES. 191 



liquid or a solid form, the internal heat not due to the 



calorific action of the solar rays was developed. 



In order to give a brief general view of the causal con- 

 nection of geological phenomena, we will begin with those 

 whose principal character is dynamic. Earthquakes are 

 distinguished by rapidly succeeding vertical, horizontal, 

 or circular oscillations. In the not inconsiderable num. 

 ber of these phenomena which I have witnessed both on 

 the old and new continents, at sea and on land, the two 

 first kinds of movement, the vertical and horizontal, have 

 often appeared to me to take place together. The mine- 

 like explosion, the vertical action from below upwards, 

 shewed itself in the most striking manner at the over- 

 throw of the town of Eiobamba in 1797, where many 

 corpses of the inhabitants who perished were hurled to 

 a height of several hundred feet on the hill of La Cullca, 

 beyond the small river of Lican. The shock is propagated 

 chiefly in a linear direction, by undulations having a velo- 

 city from twenty to twenty- eight geographical miles in a 

 minute, and occasionally in circles or ellipses of commotion, 

 in which the shocks are propagated from the center to the 

 circumference, but with diminishing force. There are dis- 

 tricts which belong to two intersecting circles. In Northern 

 Asia, where the father of history, Herodotus, ( 18 ) and at 

 a later epoch Theophylactus Simocatta, ( 181 ) spoke of 

 Scythia as free from earthquakes, I have found the southern 

 and richly metalliferous part of the Altai mountains subject 

 to the double influences of the foci of commotion of Lake 

 Baikal and of the volcanoes of the Thian-schan (" celestial 

 mountains"). ( 182 ) Where the circles of disturbance inter- 

 sect, where, for example, an elevated plateau is situated 



between two volcanoes in a state of activity, several systems 

 VOL. i. P 



