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NEW YORK STATE MUSEUM 



section of the three divisions of the Chazy limestone and the only 

 additional geologic formation present is a small point of Black 

 River limestone at the north end. The rocks are distinctly faulted 

 with some slight loss of original thickness. 



This isolated area presents an opportunity for the elaboration of 

 the geology and paleontology of a geographic unit which should 

 prove most serviceable to students of the science. 



Long Lake quadrangle. This area lies in the heart of the Adiron- 

 dacks and its rocks, as reported by Prof. H. P. Cushing, are 

 entirely of the so called Precambric formations whose precise age 

 and nature are constantly being called into qtiestion with the pro- 

 gress of knowledge. There are belts of sediments (Grenville) in 

 the southern part of the region, but the chief portion of the area 

 is constituted of eruptives and intrusives of various ages. The 

 tendency in this and other studies of what has been generally con- 

 sidered by geologists to constitute a part of the most ancient con- 

 tinental mass, is to give them a quite different interpretation and 

 to discountenance the conception that they were any part of the 

 primitive continent. 



Theresa quadrangle. This area, also under the supervision of 

 Professor Cushing, is a complicated one and presents many diffi- 

 culties to exact mapping. The Potsdam sandstone has been mostly 

 scraped off the surface and stands out only in disconnected patches, 

 15 such being exposed in an area of 5 square miles, but the 

 conditions are very favorable for determining the old rock floor on 

 which the sandstone was deposited. This floor is largely com- 

 posed of Precambric Grenville rocks. 



Highlands of the Hudson, In this complicated region present- 

 ing the southern crystalline rocks of the State, work has begun on 

 the Tarrytown quadrangle lying immediately north of the area 

 covered by the New York city folio which has been issued. The 

 formations here represented are chiefly those of the region to the 

 south, the names of which are for the most part those introduced 

 by Dr F. J. H. Merrill and as provisionally employed are the Ford- 

 ham gneiss, Poughquag quartzite, Stockbridge dolomite, Hudson 

 schist and Yonkers gneiss; the actual value of these outstanding 

 terms has yet to be determined. The formations are all closely 

 folded, faulted and sheared and the present evidence indicates the 

 sedimentary character of the basal beds of the series but there has 

 been such extensive injection of igneous granitic rocks that the 

 sedimentary aspect of the basal or Fordham rocks is greatly ob- 

 scured. The determination of the age of all the rocks must rest 



