14:2 NEW YORK STATE MUSEUM 



In like manner plant life, beginning with marine forms of low 

 type, gradually developed to the large tree ferns, sigillaria, lyco- 

 pods and equisetae of the coal measures. 



CAMBRIAN a 



Subdivisions or periods 



{Sandstone around the Adirondacks 

 Limestone in Dutchess, Washington and Saratoga 

 counties 



Acadian Limestone in Dutchess county 



p . j Roofing slates of Washington county 



& I Onnr+Tiifo in T&nt.p.TiPSS p.rmnt.v 



Quartzite in Dutchess county 



The first and lowest Palaeozoic system known in New York is 

 the Cambrian, so called from Cambria, the latin name of Wales, 

 where rocks of this age abound and were first studied by the 

 British geologist, Adam Sedgwick. Our knowledge of the Cam- 

 brian of New York is largely due to the labors of C. D. Walcott, 

 William B. Bwight, and S. W. Ford. 



The base of the Cambrian system in New York and New Eng- 

 land rests directly upon the Archaean rocks and its limit can be 

 recognized by this fact, as well as by its containing the earliest 

 known fauna. But the termination of the uppermost division is 

 not so apparent, as it grades, both in sediment and fauna, into 

 formations of the Lower Silurian system, thus showing that there 

 was no great physical change to influence the transition. North 

 of the Adirondacks the delimitation is more clearly defined. 



The strata of the Cambrian system are classified as follows: 



Upper Cambrian, or Potsdam. 



The type rock is the sandstone of the northern and eastern 

 borders of the Adirondack mountains, and correlated with it are 

 certain limestones on the south side of the Adirondacks, near 

 Whitehall and Saratoga Springs, and in Dutchess county near 

 Pougkkeepsie. The characteristic fossils are the Dikelocephalus 

 trilobites. ' 



« The descriptions of the Georgian and Acadian groups are chieflv from the 

 work of C. D. Walcott, Bulletin No. 81, U. S. Geological Survey. 



