32 The T*wo Islands. 



But the group of marine fossils that at- 

 tracts most and holds the collector's atten- 

 tion longest is that of the chambered cephalo- 

 pods. Of thisline group the highest in rank 

 are the Ammonites, a division of cephalopods 

 that was destined to become entirely extinct 

 with the close of this Cretaceous period. 

 These Ammonites were marvelously abundant 

 along the beaches of these islands and in both 

 regions small inferior forms closed the history 

 of their race. 



In the earlier periods of their history these 

 islands present themselves to the geologist as 

 twins in age, in structure and in their rela- 

 tions to the ocean in which they were set; for 

 throughout the whole time the same environ- 

 ment enwrapped both islands. A notable 

 separation occurred to them with the close 

 of the Cretaceous period. A geographical 

 barrier was destined to separate them which 

 next calls for our attention. 



Physical geography has scarcely within its 

 domain a more interesting group of facts than 

 that which goes to make up our conception 



