38 The Siskiyov Island. 



most abundant along this ancient coast line 

 was a Trigonia, one entire valve of which 

 may be seen in our illustration, surrounded 

 by hundreds of fragments of others broken 

 by the surf, then covered by scanty sediment 

 and so assigned a permanent place in this 

 rock. These shells were multiplied and others 

 were rapidly added, until marine life filled 

 every available nook of the whole coast line 

 of the island. The geological period whose 

 beginning is thus marked, was the Cretaceous. 

 That is to say, the period at which these shells 

 lived was that in which the chalk of France 

 and England was deposited. 



In other words, at the time when the great 

 body of Europe was yet under the deep sea 

 that was slowly depositing in its profoundest 

 depths this chalk, the far-off Siskiyou island 

 was surrounded by this ancient sea beach, on 

 which these shells struggled for life. Later 

 deposits on this beach as seen in layers a few 

 feet higher and therefore more recent, show 

 a notable change of material as well as fossil 

 contents. 



