8 PALEONTOLOGY OF NEW-YORK. 



differing little in its general characters from the Potsdam sandstone which 

 lies below, except perhaps in a lighter color and more friable and in- 

 coherent texture. 



So far as observed, there are no alternations of the Calciferous with the 

 sandstone which succeeds it ; though where the former is broken up, and 

 presents the brecciated character before described, fragments of the higher 

 sandstone are mingled in the interstices throughout the rock below. There 

 are, moreover, sometimes evidences of faults or down-throws of the lower 

 rock, by which the higher sandstone is brought into a lower position. 



In its eastern extension, this upper sandstone thins out somewhere in 

 the northern part of Wisconsin, or the adjoining State of Michigan, since 

 it has no existence in a section along the Escanaba river, on the north of 

 Lake Michigan. It may also be stated, that in the general thinning out of 

 all the lower limestones, the Chazy limestone is scarcely recognized west 

 beyond the great northern curve of these rocks about the head of Lake 

 Michigan. 



It will be observed, therefore, that this upper sandstone of the west 

 holds in the series precisely the place of the Chazy limestone, as will 

 appear on comparing the column of strata in New- York with that in the 

 west : 



Nkw-York. Iowa, Wisconsin and Minnesota. 



Trenton limestone. 



Black-river limestone. 

 Birdseye limestone. 

 Chazy limestone. 

 Calciferous sandstone. 

 Potsdam sandstone. 



Trenton limestone. 

 Galena limestone. 

 Black-river limestone. 

 Birdseye limestone. 

 Sandstone of the Chazy period. 

 Calciferous sandstone. 

 Potsdam sandstone. 



While in New- York and Eastern Canada the conditions giving origin 

 to the Calciferous sandstone were succeeded by seas capable of sustaining 

 a numerous fauna, with coral reefs and all the phenomena attendant upon 

 the great limestone formations, this period at the west was followed by 

 precisely a repetition of the conditions which preceded the deposition of 



