CALCIFEROUS SANDSTONE. 121 



of the cast side, are quite heterogeneous in their composition. This may be explained 

 partly on the ground that the materials were derived from that remarkable system which 

 lies adjacent to it upon the east. Some of the insulated masses upon this eastern range 

 present us with a combination of products resembling the calciferous, birdseye and trenton; 

 in which, too, the forms of the fossils are such that it is at first sight difficult to determine 

 to which rock they are to be referred, a fact which fully corroborates the opinion that all 

 the limestones of this group may be very properly included under one name. Even the 

 Bellcropfion bilobatus, which has been credited to the Trenton limestone, often occurs in 

 the Calciferous sandstone. 



A locality of this rock, in which there is a combination of the several limestones of the 

 Champlain group, exists opposite to the city of Albany in Grecnbush, crowning a remark- 

 able knob near the site of the Old Cantonment ; but in other places the line of distinc- 

 tion between the masses is quite evident, and from those localities one would infer that it 

 is quite proper to keep up a distinction of the masses. In these instances, certain fossils 

 are limited to the masses ; and they often appear to be cut off suddenly, on some distinct 

 change in the composition of the rocks. 



Range and extent. The Calciferous sandstone covers a wider area than the Potsdam 

 sandstone. It is, in the first place, coextensive with the potsdam ; but in addition to this 

 it passes through the Mohawk valley, where the latter is hardly known. In the counties 

 of Dutchess and Orange, it forms an imperfect belt. In Columbia, Rensselaer and Wash- 

 ington counties, its continuity is still more broken. It occupies, in the three last counties, 

 the knobs, as at Greenbush, Greenwich and Whitehall. These knobs lie contiguous to 

 the valley of the Hudson : it is, however, still sparingly found twenty miles east of the 

 Hudson river, as at Hoosic ; and, as I now believe, near Pownal in Vermont, forming at 

 the latter place heavy beds of siliceous limestone, which are peculiarly attractive by their 

 bold broken outlines and perpendicular walls. Probably this broken range or belt runs 

 obliquely across Columbia and Dutchess counties, and thence onw T ards through Orange, 

 crossing the Hudson river a few miles above Newburgh. 



We can hardly avoid the inference that this belt was once continuous, and formed an 

 important mass, overlying the Taconic slate. At one period it undoubtedly was conti- 

 nuous with the same rock which passes through the Mohawk valley, and onwards to the 

 northwest through Jefferson and St. Lawrence counties, and thence over wide tracts in the 

 Canadas and the region of Lake Superior. 



In the Hudson valley, the indications of its former extent are found in the insulated 

 patches, which sometimes crown the highest knobs of the region ; but then as the forces 

 which occasioned the great northern fractures of this valley, disturbed and broke up the 

 rocks unequally, we find it sometimes in the vallies outcropping from beneath the Hudson 

 river slates, which have been preserved from denudation. These patches vary much in 

 extent : some are limited to a few acres ; others extend several miles, but they are quite 

 insulated, and may be observed on all sides. At favorable points, the position they occupy 

 need not be mistaken. They rest upon the slates of the Taconic system. 

 [Agricultural Report.] 16 



