166 



PALEOZOIC TIME. 



Fig. 21,6 is an ideal section of the rocks of New York, along a line 

 running southwestward from the Archaean on the north across the State 



to Pennsylvania. It shows the relative positions of the successive 

 strata, — bringing out to view the fact that the areas on the preceding 

 map ai'e only the outcrops of the successive formations. This is all the 

 section is intended to teach ; for the uniformity of dip and its amount 

 are very much exaggerated, and the relative thickness is disregarded. 



A. LOWER SILURIAN. 



I. PRIMORDIAL PERIOD (2). 

 1. American. 



The Primordial or Cambrian Period in North America includes two 

 subdivisions, distinct in their fossils, according to present knowledge. 



(1.) The Acadian Epoch, including the St. John group of Matthew 

 (Acadian group of Dawson), of St. John, New Brunswick, and other 

 rocks of eastern Newfoundland. 



(2.) The Potsdam Epoch, or that of the Potsdam sandstone, of 

 Potsdam, in the northern part of St. Lawrence county, N. Y., and its 

 equivalents elsewhere ; and also of the Georgia and Swanton slates 

 and Winooski limestone of western Vermont, and sandstone and lime- 

 stone near Troy, N. Y. The Acadian beds in Newfoundland lie un- 

 conformably beneath those of the second epoch. 



I. Rocks : kinds and distribution. 

 Primordial rocks have been observed over various parts of the 

 North American continent, both adjoining the Archaean regions of 

 New York, Canada, and elsewhere (where they bear every evidence 

 that they were formed on the shores of the Archaean lands), and also 

 distant from them, where in some places they were made in the deeper 

 continental seas. They occur on the eastern border of the continent, 

 in Newfoundland, Nova Scotia, New Brunswick, and eastern Massa- 



