GEOLOGY OF THE NORTH CREEK QUADRANGLE 9 



Pregrenville masses were either engulfed by the later great in- 

 trusions or that they were changed beyond recognition. 



Areal distribution of the Granville. About four-ninths of the 

 surface rock of the quadrangle is Grenville, provided we include 

 the Grenville which makes up considerable portions qf the areas of 

 mixed gneisses. It should be noted that the Grenville here as- 

 sumes much more prominence than is usually the case in the Adi- 

 rondacks. Also, as the accompanying map shows, the Grenville 

 is very widespread in its distribution, it being least prominently 

 developed in the central and northern portions. A striking feature 

 is the " patchy '' character of its distribution, this being due to 

 the very irregular manner in which the great igneous intrusions 

 broke through and cut to pieces the Grenville strata. 



The three types of Grenville which are sufficiently different to 

 allow of separate representation on the geologic map are : 



1 Crystalline limestone which is generally associated with dark 



hornblende gneiss, this latter rock often being garnetiferous. 



2 Quartzite in thin to thick beds and usually more or less inter- 



bedded with thin layers of biotite gneiss or sometimes a little 

 limestone. 



3 Other gneisses, chiefly gray feldspar-garnet or dark gray biotite- 



garnet-feldspar or white feldspar-gneiss. Occasionally a 

 little limestone, quartzite, or hornblende-gneiss may occur 

 closely associated, especially where the glacial drift is heavy. 



The largest area of Grenville occupies the western portion of 

 the quadrangle and by far the greater part of it consists of lime- 

 stone and its associated hornblende gneisses. A considerable area 

 of quartzite lies south of Sodom and a smaller one east of Little 

 moimtain. The only distinct area of mica-feldspar gneiss covers a 

 few square miles south of Thurman. 



Toward the southeast occur two irregular shaped areas of Gren- 

 ville which are almost entirely made up of limestone and associated 

 hornblende-garnet gneiss, the limestone being especially thick and 

 well shown in outcrops just west of the Potter-Birch mountain 

 ridge. 



The large and very irregular shaped area along the eastern side 

 of the sheet consists mostly of various gneisses with one consider- 

 able area of quartzite south of Pottersville and another east of 

 Chase mountain. The only mappable limestone belt there is a small 

 one extending eastward from Valentine pond. 



