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NEW YOKE STATE MUSEUM 



the Potsdam sandstone, and were called Taconic. This range of 

 rocks contains very few fossils or none in most localities, and 

 geologists have been obliged to study it without the aid which 

 fossils, would have given in explaining the relation and true posi- 

 tion of its confused and contorted strata. The general conclu- 

 sion has been that this series of strata is not a separate and 

 distinct one, but merely the eastward extension of the rocks older 

 than the Medina and Clinton groups, changed in character or 

 ' metamorphosed ' by the effect of heat and pressure. The work 

 of Walcott and others has proved that most of the schistose rocks 

 are of Hudson river age, though a portion of them contain Lower 

 and Middle Cambrian fossils and are therefore distinct. 



In Westchester and New York counties, rocks of Hudson river 

 age cover large areas. They are, however, metamorphosed into 

 mica schist and contain no fossils. 



Life of the Lower Silurian 



The animal life of this system was also marine and chiefly 

 represented by sponges, corals, brachiopods, mollusks and crus- 

 taceans. Cephalopods were the dominant forms^ and were of 

 great size. Fishes have recently been announced by C. D. Wal- 

 • cott. No land animals are known to have existed except some 

 insects reported from Europe. Vegetable life was represented 

 by sea weeds, though a land plant has been found in Great 

 Britain. 



UPPER SILURIAN SYSTEM 

 The Upper Silurian system, which is the upper division of the 

 original Silurian system, consists in New York state of the fol- 

 lowing divisions: 



System Group 



f Lower Helderberg 

 Onondaga Salt Group i J^terlime 



Upper feilunan <{ Niagara 



Clinton 



Medina 



. Oneida 



