344 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



south in a broad belt, and constitutes the west shore of the great cur- 

 vature of Lake Michigan, called " Green Bay." 



From hence this vast sheet of Trenton Limestone proceeds south- 

 ward, at some distance from Lake Michigan, and near Jonesville, 

 Jefferson County, bifurcates, — one branch running off west, to cross 

 the Mississippi, while the other, narrower, after a course of about 

 1 50 miles, is lost under the drift of Illinois. The whole length of this 

 northern outcrop is 1700 miles. 



To give some idea, however inadequate, of the eastern outcrop of 

 this stratum, we may state, that, due south from Montreal in Canada, 

 Trenton Limestone passes in long strips down both sides of Lake 

 Champlain, and on the east side of the Hudson River, which it 

 crosses near Newburg, to run S.S.W., as a rather broad band, in its 

 proper geological position, to nearCentreville in Alabama, — a distance, 

 from Montreal, of about 1130 miles. 



Of the broad areas of Trenton Limestone in Tennessee and the 

 south-west, we may not now speak. In the north-west portions of 

 New York in the counties of Jefferson, Lawrence, &c, this limestone 

 occupies much surface, and with very circuitous outlines on account 

 of the unevenness of the country. Together with Chazy Limestone 

 it passes from the Black River to Oneida County, and from thence 

 to Spruce Cradle, Steuben Creek, Beaver Meadow Creek, Stittville, 

 and Holland Patent. 



On the north and south sides of Little Falls it appears in patches. 

 Further particulars are here inadmissible. 



Position. — Although usually in a kind of wavy horizontality, it is 

 subject to uplifts along the Mohawk Valley, as well as at Baker's 

 Falls and Glenn's Falls in the Hudson Valley. 



Thickness. — This is 400 feet at Chazy on Lake Champlain ; 300 

 feet in Lewis County, and much thinner elsewhere, especially at- 

 tenuating from west to east (Vanuxem). 



Fossils. — See General Table. This stratum is very fossiliferous, 

 and contains 256 species, being not very far short of one-third of 

 the whole fossils of the Silurian series. 



The numerical Table, No. II., shows us that this rich stratum con- 

 tains 3 species of Plantse, 15 of Zoophyta, 10 each of Bryozoa and 

 Echinoderms, 72 of Brachiopoda, 16 of Monomyaria, 19 of Di- 

 myaria, 25 of Trilobites, 37 species of Gasteropoda, chiefly Pleuro- 

 tomarice and Murchisonia, 44 of Cephalopoda, chiefly Orthocerata. 



The Brachiopoda, besides being numerous, are constant and 

 reliable over great areas ; but most of them end as species with the 

 group, seventeen only surviving. The Lingulce are the half of the 

 whole genus found in the Silurian system. 



" Near the base of Trenton Limestone the Orthoceras is very rare, 

 while the few species of Cyrtoceras known in this rock seem almost 

 confined to that position. As we ascend in the strata, Orthocerata 

 are occasionally found, but never abundantly, in the lower half of 

 the deposit. In the centre of the rock the Orthoceras increases in 

 numbers, and in the succeeding beds they are massed together in 

 myriads. In the highest beds of this limestone in many places they 



