L36 //. P. Gushing — Lower Paleozoic Hooks of JVew York. 



surface exposures are concerned, to the immediate vicinity of 

 Saratoga. 



The Potsdam and Little Falls are the only two absolutely 

 conformable formations in the entire early Paleozoic section 

 of New York. In all other cases there is an unconformity 

 between formations and frequently between subformations. 

 To draw the line between Cambrian and Ordovician at this 

 horizon is thus to draw it at the one place where there was 

 continuous deposition between two formations. Structurally 

 and faunally the Potsdam and the Little Falls belong to the 

 same system and group. Their normal affiliations are with 

 one another. And there is no diastrophic warrant whatever 

 for putting a systemic boundary between them. 



The Beekmantown Group. 



In this paper just cited, Ulrich and dishing separated from 

 the Little Falls dolomite the upper division, heretofore classed 

 with it, which Vanuxem called the "fucoidal beds," and which 

 careful reading of his report shows that he would himself have 

 separated as a distinct formation, had his district alone been in 

 question. The name proposed for this new division is the 

 Tribes Hill limestone. It is much more calcareous and more 

 fossiliferous than the Little Falls, and there is a distinct and 

 ■widespread break between the two. Ulrich regards the fauna 

 as of earliest Beekmantown age, and on the basis of his deter- 

 mination the line between the Beekmantown and Saratogan is 

 drawn at this break. This formation is the only representa- 

 tive of the Beekmantown which occurs on the south and west 

 sides of the Adirondack shield. 



In the Cham plain valley Brainard and Seely some years ago 

 divided the Beekmantown into five subdivisions, which they 

 lettered from A to E.* The equivalence of division A and 

 the lower half of B with the Little Falls dolomite, and the 

 impropriety of classing them as Beekmantown at all, having 

 now been shown, there yet remain the upper three and one- 

 half divisions, with a thickness of from 1300 to 1400 feet. 

 The thorough faunal study of this formation, and its proper 

 subdivision and naming, constitute the most important problem 

 which awaits the investigator of the early Paleozoic rocks of 

 New York. It is reasonably certain that the four lithologic 

 divisions of Brainard and Seely will require much readjust- 

 ment, when the faunas are collected and studied, and it would 

 be folly therefore to give them names as at present constituted. 



It is not known whether the Tribes Hill limestone is pres- 

 ent in the Champlain valley or not. If it be, it is represented 

 *Bull. Am. Mus. Nat. Hist., vol. iii, pp. 1-23. 



