CALCIFEROUS GROUP. 
3d 
shows that thermal action existed; and there appears to be little doubt that the springs now 
in action, such as the Hoosick, the Buncombe in North Carolina, the Virginia and the 
Arkansas, have their source at the bottom of this rock, whose range extends northeast and 
southwest through the Atlantic States, though with some considerable change of character, 
being in thicker and more regular layers, of a grey or blue color, and a purer limestone. 
Fossils are extremely rare in the calciferous rock in the third district: all that have come 
under notice, or been heard of, are two lingulae of unknown species, found at Little-Falls. 
None were seen there by myself, except a single fragment of a spiral univalve, resembling a 
common turretted shell, which, when whole, was probably an inch and a half in length, and 
another fragment resembling an orthostoma. At the east end of the Noses, on the north 
side, and at the top of the cliff near the river, two or three small casts of univalves were 
found, but too imperfect to determine the species or even the genera. 
A rolledstone of this rock was found by Dr. Eights in Saratoga county, containing the 
Lingula acuminata. They covered the surface of the fractured parts, showing from sixty 
to seventy valves in an area of three by two inches. 
From the loose texture of the rock in many of its parts, it was highly favorable for the per¬ 
colation of water, many of its products manifesting that action; which doubtless may have 
destroyed many of its fossils, though very probably but few were deposited with its materials, 
the rock being a very extensive one in the other States, in all which, with one known excep¬ 
tion, it is wholly non-fossiliferous. 
Fucoidal Layers. These layers are well defined, and readily distinguished from the calci¬ 
ferous rock by their disposition in thick strata; many parts of which, when long exposed, 
show a structure as if formed of numerous thin ones. The mineral composition is more 
varied, showing frequently a mixture of the calciferous sandrock and the birdseye limestone, 
the latter rock being the successor to this group. It often presents ramose forms, usually 
composed of the calciferous portion: where these exist, there is always more or less shale 
associated with them. These forms are frequently so imitative, that it is often difficult to 
distinguish them from the fucoids, which are numerous in these layers, but rarely sufficiently 
distinct to determine more than their organic nature. 
In parts the rock resembles a breccia, but of rounded particles, generally of compact 
limestone like the birdseye, and enveloped usually by a crystalline limestone. The particles 
are of various forms, as flat, round, etc. ; they are evidently accretions, parts of which were 
thin layers broken up, partially dissolved, and cemented together. The character of the 
layers varies in different places, the parts of which they are composed varying as to propor¬ 
tion, crystalline action, etc. 
Besides fucoids, it contains other fossils, many of which are peculiar to the rock: they 
appear to be more numerous where the birdseye mixture exists. The annexed wood-cut 
exhibits four of the most characteristic fossils of the group. The whole are of interest, 
being the lowest fossils of any discovered in the third district. 
