GEOLOGY OF THE BLUE MOUNTAIN QUADRANGLE 33 



Blue ridge, is in most respects very typical of central and southern 

 Adirondack mixed gneisses. Throughout the area various types of 

 Grenville strata have been more or less cut to pieces by pink granite 

 or granitic syenite, the dips generally being very steep and the 

 igneous masses having nearly always penetrated the Grenville 

 parallel to the foliation. More rapid wearing away of the weaker 

 Grenville belts accounts for the arrangement of low ridges approxi- 

 mately parallel to the foliation. Many exposures show either pure 

 Grenville or pure granite, while in many others the granite and 

 Grenville are more or less intimately associated, in some cases local 

 assimilation having taken place. Excellent outcrops in the open 

 field between Blue Mountain Lake village and Crystal lake afford a 

 practical demonstration of the very intimate relations of granitic 

 and Grenville gneisses with some intermediate rocks due to mag- 

 matic assimilation. The granites are pinkish to grayish and rather 

 variable though always gneissoid. In certain outcrops gray, biotite 

 or dark garnet or pyroxene, Grenville gneisses may be seen to grade 

 into the igneous rock with no visible contacts. In a few cases the 

 contacts are fairly sharp. Most of the exposures, however, con- 

 sist of rocks of distinctly intermediate character which are clearly 

 the products of local assimilation. 



Area south to southwest of Grove (Deerland). This body of 

 mixed gneisses, covering about 2 square miles, mostly comprises 

 outcrops of gray to pinkish granitic to syenitic gneisses filled with 

 streaks or inclusions of dark to light-gray gneisses (presumably 

 Grenville), the rocks being crudely banded, very gneissoid, and 

 often considerably contorted. 



Exceptional exposures occur as big ledges in the bed of the stream 

 which is the outlet of South pond. The rock, instead of. being 

 distinctly gneissoid to banded, is streaked or wavy as though small 

 amounts of dark Grenville had been partially fused and assimilated 

 by syenite magma, the syenitic character being preserved in spite 

 of the inclusions. The whole presents what might be 'termed a 

 *' marble-cake " appearance. 



Area across the northern portion of the quadrangle. This area 

 of about 12 square miles extends completely across the northern 

 portion of the quadrangle and is apparently the southern border 

 of the so-called " Long Lake gneiss " as mapped by Gushing in the 

 region immediately to the north. For most part the rocks of this 

 area are rather typical mixed gneisses, that is, they are largely 

 granite or syenite more or less intimately associated with Grenville, 



