CALCIFEROUS GROUP. 35 



shows that thermal action existed ; and there appears to be httle doubt that the springs now 

 in action, such as the Hoosick, the Buncombe in North Carohna, 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 hngulse 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 

 foimd, 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-fossilifcrous. 



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, showring 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 Ccilciferous 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 

 distinguisli 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. 



