walcott.] ADIRONDACK SUB-PROVINCE. 203 



the transition limestone and never in the northern district alternates with it, but 

 always holds the relation of an inferior rock.' 



This rock is a true sandstone, of red, yellowish red, gray, and grayish white 

 colors. It is made up of grains of sand and held together without a cement. Inter- 

 mixed with the siliceous grains are finer particles of a yellowish feldspar, which do 

 not essentially change the character of the sandstone, but they show the probable 

 source from which materials forming it were originally derived, viz, some of the vari- 

 eties of granite. Unlike, however, most of the sandstones, it is destitute of scales of 

 mica. The coloring matter of the rock is evidently oxide of iron, but unequally 

 diffused through it, giving it intensity or deepness of color in proportion to its quan- 

 tity. In some places it is almost wanting, which makes it, when pulverized, a good 

 material for glass. The grains and particles in its composition are generally angular, 

 but where it takes the character of a conglomerate, as it does in the inferior layers, 

 they are frequently rounded. The thicker strata exhibit an obscurely striped appear- 

 ance, owing to prevalence of certain colors iu the different layers. 8 



In the description of the sandstone on the Lake Champlain side in 

 Essex County it is said : 



This I consider the same formation I have described under the name of the " Pots- 

 dam sandstone." Its position is evidently beneath the Transition limestone and Calcif- 

 erous sandrock. It is very deficient in organic relics, though not entirely destitute 

 of them. It is unnecessary to repeat what has already been said of this rock ; it is 

 purely quartzose or siliceous in its composition and finely stratified. It dips to the 

 northeast at Port Kent, at an angle varying from 5° to 10°. The places where it 

 occurs along Lake Champlain are indicated on the map of a part of this county, to 

 which I refer the reader. This rock at Keeseville has been rent in the most remark- 

 able maimer ; several fissures, the principal one of which extends nearly a mile, and 

 through which the An Sable flows, have been opened by some convulsion in nature to 

 the depth in some places of 100 feet, aud from 5 to 20 feet wide. Near the bottom of the 

 fissure at the High Bridge, as it is called, I discovered numerous specimens of a small 

 bivalve mollusoa, a Lingula. I found also, on examination, that the same fossil oc- 

 curred through au extent of seventy feet at least, and so far as I could discover it was 

 the only fossil inclosed in the rock. It is extremely thin and delicate, yet the shell 

 is perfectly preserved, and is probably one of the oldest inhabitants of the globe, as 

 the rock in which they occur is the oldest of the transition series. 3 



In the second annual report of the paleontological department of the 

 New York survey Prof. T. A. Conrad tabulated the formations to show 

 the order of superposition aud some characteristic fossils in the tran- 

 sition strata. On the primary occurs No. 1, formed of variegated sand- 

 stones (Potsdam sandstone of Emmons), and the olive sandstones and 

 slates, characterized by Fucoides serra. These are classified under the 

 Cambrian system of Prof. Sedgwick. 



The base of the Lower Silurian is a gray calcareous sandstone, char- 

 acterized by Lingula acuminata. This part of his table is as follows: 4 



LOWER SILURIAN STRATA. 



Gray calcareous sandstone Lingula acuminata 



1 Op. cit., p. 214. 

 2 0p.cit.,p.215. 

 s Op.cit.,p.230. 



* Second annual report of the paleontological department of the survey. Third annual report of the 

 geological survey of New York. Albany, 1839, p. 63. 



