lO NEW YORK STATE MUSEUM 



A patch of Grenville gneiss lies at the extreme northwestern 

 corner of the sheet and another at the northeastern corner, while 

 a belt of limestone just enters the northern map limit at the Nat- 

 ural Bridge. The Grenville around Loon lake consists mostly of 

 white to gray gneisses. 



A number of small patches of Grenville are shown within the 

 igneous rock areas and these usually represent actual inclusions 

 of the Grenville which are large .enough to be indicated on the 

 map. No attempt has been made to show the many smaller in- 

 clusions. The Grenville occurring within the areas of mixed 

 gneisses will be discussed in connection with those gneisses. 



Grenville types. The Grenville types are described in consid- 

 erable detail because, in the writer's opinion, if the broader struc- 

 tural and stratigraphic relations of the Grenville series are ever 

 to be worked out, it is necessary to have these rocks carefully 

 descriped and mapped over a much larger area than that of a single 

 quadrangle. When a number of the other quadrangles of the south- 

 eastern Adirondacks, in addition to those of Broadalbin, Saratoga, 

 and North Creek already published and the Lake Pleasant now 

 being studied, are mapped in detail, it is quite possible that some 

 of the larger structural and stratigraphic features may be made 

 out. 



Crystalline limestone. In common with the Newcomb and the 

 southern portion of the Schroon lake sheets, the limestone of the 

 North Creek sheet is much more prominently developed than is 

 usual in the southeastern Adirondacks. The numerous outcrops 

 of limestone (actually observed) are indicated on the accompany- 

 ing map. 



Perhaps the most abundant variety is a nearly white, medium to 

 coarse crystalline, very calcitic limestone through which are scat- 

 tered numerous flakes of graphite and phlogopite or biotite and 

 occasional specks of pyrrhotite. The calcite crystals range from a 

 few millimeters to fnore than a half inch across, while the graph- 

 ite flakes are commonly several millimeters across. Other crystals 

 less often seen in this rock are pyrite, nearly colorless pyroxene, 

 and brown tourmaline. Rarely the limestone is rather dolomitic. 

 This variety of limestone appears in many excellent exposures, the 

 most extensive outcrops perhaps being on the small hill just south 

 of Daggett pond. 



A second very common variety is nearly white, medium to 

 coarse-grained calcitic and with numerous irregular shaped, pel- 

 lucid quartz grains, flakes of graphite, and specks of pyrite or 



