THE PHYSICS OF THE EARTH. 



219 



the theory of a rounded arch would require. Thus we may not 

 only explain the folds of the Alps, but also recognize that the folds 

 both above and below were less extensive than was formerly sup- 

 posed ; and this greatly simplifies the labor of the geologist in re- 

 storing the former structure of mountain chains as they appeared 

 before thev were greatlv eroded. 



dectm OF /forth AmencA,£a.st to WeU (Dana). 



A 





Section of douth America, Ed5t to YVebt /Dsna). 



dectionofAsia., A'orth to douth (Dans). 



5ectmoFAfrica,/^orth to douth (Dana). 



Sect/on oP AFricA £ast to /Vest (Pava^. 



Hiwal^Yas 



Tibeta.n Table lariO. 

 flips 



Fig. 12. Sections of the Continents, and of the Alps and Himalaya on the 

 same Scale. (Gen. Strachey. ) 



The process of undermining the sea bottoin in the expulsion of 

 lava arising from the leakage of the ocean, has given rise to all the 

 important folds of the earth's crust. Thus arose all the complicated 

 folds in the Alps, Andes, Alleghenies and other mountain ranges. 

 And wherever we see these folds sea trenches once existed, and the 



