EXERCISES. 47 



mountains, or entombed them deep within the earth itself 

 Again : it was observed that marine shells were associated 

 in one spot, and the fresh- water kinds in another, and that 

 similar genera and species were in like manner separated 

 and arranged, although it was obvious that the flood here 

 contemplated must have heaped all kinds promiscuously 

 together. And, when at length more extensive observation 

 showed that the same locality exhibited alternations of marine 

 and fresh-water deposits it was felt that no single event 

 was adequate to produce such varied effects ; and hence arose 

 the more extended views of the operations of nature which 

 constitute the principles of modern geology. 



