EXTINCT ANIMALS 



is the rule and not the exception. It is rare 

 for the strata to He in a strictly horizontal 

 position. The crust of the earth is continually 

 being slowly pushed up or down, and as it were 

 " crumpled " or thrown into wave-like folds. 

 The cause of this crumpling is to be found in 



Fig. 34. — Tilted strata of the chalk at Sea ford, Sussex. J^hoto- 

 graphed by Messrs. Dollnian Bros. 



the shrinking of the earth and the movements 

 of subterranean steam — causing earthquakes 

 and other earth movements. The " crust " of 

 the earth is a mere skin. If we bored twenty 

 miles into it we should come to immensely hot 



50 



