GEOLOGY OF THE LONG LAKE QUADRANGLE 459 



rangle being some 400 feet in all probability. The altitude has 

 since slowly increased to its present amount, and the upward move- 

 ment may yet be in progress. 1 



ROCKS 



With the exception of the glacial deposits and boulders, and later 

 stream and lake accumulations, all the surface exposures occurring 

 in the quadrangle exhibit crystalline rocks of Precambric age. 

 These comprise not only considerable belts of the sedimentary 

 Grenville rocks, and great batholitic masses of anorthosites, syenites, 

 granites and gabbros, considerably younger than and intrusive into 

 the Grenville rocks, but also large areas of gneisses, which seem for 

 the most part igneous, which can not yet be classified, but which 

 are, at least in part, older than the great intrusions. 



Grenville rocks. The most extensive belt of Grenville rocks 

 occurring within the quadrangle's area has its broad northern end 

 penetrated by the upper part of Follensby pond, down whose shores 

 it runs for } mile, with greatest breadth on the west side. It ex- 

 tends southward from Follensby to the Moose creek valley, curving 

 toward the southwest as it approaches it, and extends up this valley 

 and its continuation, the Bog stream valley, to the west edge of the 

 quadrangle. 2 As it runs west it narrows to a breadth of less than a 

 mile, which is less than half the average breadth south from Fol- 

 lensby. This will hereafter be referred to as the Moose creek belt. 



Another considerable belt of Grenville rocks runs west and north- 

 west from Round island, in Long lake, past Rock pond and Grampus 

 lake to the quadrangle edge, with an outlying small area to the 

 south running west from Grampus lake. No trace of undoubted 

 Grenville rocks could be discovered on the east shore of Long lake, 

 opposite Round island, doubtful gneisses constituting that district. 

 This will be called the Rock pond belt. 



A third belt is crossed by the Raquette river just below Long lake, 

 and extends up Cold river some 2\ miles. This very likely extends 

 down the Raquette to a connection with the Moose creek belt, but 

 lack of outcrops in the interval save for a few meager exposures of 

 doubtful igneous gneisses, renders the matter uncertain. This is the 

 Cold river belt. 



There is a considerable area of Grenville rocks about the lower 



1 For a fuller account of the geologic history of the region see N. Y. State Mus. Bui. 95. 

 p. 272-94. 



2 See accompanying map. 



