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NEW YORK STATE MUSEUM 



Life of the Cambrian 

 So far as we know, the life of the Cambrian was wholly marine. 

 No vertebrates are known to have existed. The Brachiopods 

 were small. The Lamellibranchs, so far as known, were also very 

 small. There were representatives of the groups of Pteropods 

 and Gastropods. Cephalopods appeared in the Upper Cambrian. 

 There were also sponges, and corals. The trilobites, however, 

 were the only forms which had attained large size or high de- 

 velopment. Besides these were some other articulates, the 

 Ostracoids and Phyllopods, and probably some worms. The 

 plants were sea weeds. 



LOWER SILURIAN OR ORDOVICIAN 



This system is a subdivision of the original Silurian system 

 which received its name from that of the Silures, an ancient race 

 inhabiting the eastern part of Wales, where Sir Roderick Mur- 

 chison studied these rocks in detail. The second name was de- 

 rived by the British geologist Lapworth from that of the Ordo- 

 vices, also an ancient British tribe. 



In New York this system is well developed and includes the 

 following subdivisions: 



System Group Stage 



I Hudson river shale and sandstone 

 [ Hudson river < 



( Utica slate 



( Trenton 

 Lower Silurian \ ^^ \ Black river 



i Birdseye 

 I Chazy 



I Calciferous 



Calciferous Group 



Overlying the Upper Cambrian or Potsdam sandstone at many 

 points is another, which contains a considerable proportion of 

 lime mingled with it, and from this fact has received the name of 

 the Calciferous sandrock. 



It may be described as a silicious or gritty limestone, generally 

 of a brownish color, lying in straight, thin layers, and attaining 



