272 Dr. Bigsby's Sketch of the Topography 



common on the Hudson and on Lake Champlain. It skirts 

 the ridges of gneiss at the margin of all the valleys among 

 Macomb's Mountains, and entii-ely surrounds the spurs of 

 gneiss which cross the Erie Canal at the Little Falls and the 

 Noses *. 



Carhoniferous Limestone. — Following the series upwards, 

 the next rock we arrive at is the metalliferous limestone of 

 Eaton, which is the " carboniferous " of Conybeare and Phil- 

 lips, and the " intermediaire" of D'Aubuisson in every respect 

 but its exti'emely small inclination. Eaton defines it thus : 

 It is " more or less compact, opaque, fi'acture conchoidal and 

 scaly. It is frequently cellular, containing small disseminated 

 masses of calcspar in scales. It is sometimes slaty, but then 

 each lamina or layer is compact. It is not traversed by veins 

 of calcspar, like sparry lime-rock ; a kind of bark -like fer- 

 ruginous slate is often interposed in the natural cleavages. Its 

 upper surface contains petrifactions. Colour generally gray 

 or slate colour f." 



This rock " is nearly co-extensive with the calciferous sand- 

 rock ; wherever the sandstone skirts the ridges of gneiss, the 

 limestone overlays it, generally commencing from one to three 

 or four miles from the foot of the gneias range." — (G. S. p. 82.) 

 " It forms a large band stretching to the north-east end of Lake 

 Ontario|, in a curvilinear course, from the point of (Little) Fall 

 Hill, by the way of Fairfield, Newport, Trenton, &c., with its 

 south margin about eight miles N. of Utica, and ten miles N. 

 of Rome." — " In all this extent it is separated from the se- 

 condary rocks by a belt of grauwacke, under which it passes 

 at its south-western edge." — (G. S. p. 83.) 



Mr. Eaton does not mention the position of its strata. At 

 the east end of the lake they are nearly horizontal. Professor 

 Renwick found them so at Trenton also. 



Grauisoacke next succeeds, according to Mr. Eaton, and is 



• A pass of the Mohawk between high hills, 26 miles E. of Little Falls. 



f Geological Survey, p. 33. 



Professor Renwick of New York, in vol. ii. p. 186 of the Annals of the 

 Lyceum of that city, has given the following sketch of the mineral character 

 of this rock, at Trenton Falls near Utica, a part of the tract traced by Eaton; 

 considering it to be the submedial limestone of Conybeare : — At this place 

 the strata are open to view for a depth of three hundred feet. They are 

 of various thickness, and are parted by thin seams of tu"gillaceous matter. 

 The higher layers are composed of carbonate of lime, nearly pure, of a light 

 gray colour and crystalline structure, easily separable into rhombic crystals. 

 At greater depth, the substance becomes more compact, of a darker gray 

 colour, and finally quite black : it is then highly foetid. The lower strata 

 are susceptible of a high polish. Fossils are very abundant, and in some 

 cases form nearly the whole mass. 



X I have seen it in situ at Sackct's Harbour. 



described 



