454 NEW YORK STATE MUSEUM 



texturally and structurally, by action of great compressive forces, 

 so much so that many of them have lost all trace of their original 

 character. These four groups are , 



1 A series of old sedimentary rocks, the Grenville series, much 

 involved with igneous rocks some of which seem of approximately 

 the same age. 



2 A series of gneisses which seem to be mainly or wholly of 

 igneous origin, which may be, in part, older than the Grenville 

 rocks, though no certain evidence of this has yet been forthcoming 

 in the Adirondack region. If there are in the region any exposed 

 rocks more ancient than the GrenAdlle rocks, they are here. 



3 A series of igneous rocks, usually in great masses (batholites) , 

 which are demonstrably younger than both the preceding, and 

 which are not so profoundly changed in character, retaining often 

 traces of their original textures and structures. 



4 A series of very much younger igneous rocks which have under- 

 gone- little change since their intrusion. 



Rocks belonging to all four of these groups are found within the 

 area of the Long Lake quadrangle, and all but the last have an ex- 

 tensive representation, the quadrangle being rather unusual in this 

 respect. 



Grenville series. Here are classed certain well banded gneisses 

 and schists, some of them very quartzose and grading into quartz- 

 ites, with bands of varying thickness of coarsely crystalline lime- 

 stone. They are believed to be old water-deposited rocks, ancient 

 vsheets of sand, mud and calcareous mud deposited on the floor of 

 some large body of shallow water, in all probability the sea. There 

 is apparently a great thickness of these rocks, but neither their base 

 nor summit is known, and they are so disturbed, and usually so 

 poorly exposed that our ideas concerning their thickness are of the 

 vaguest. They must have been deposited upon a floor of older rocks, 

 but we are at present ignorant as to what these rocks were, and 

 whether or not they are anywhere exposed in the district. 



Because of the thickness and the frequent changes in the char- 

 acter of the deposit it is certain that the deposition of these rocks 

 took a long time, pointing to a protracted submergence of the area 

 at this early day, with frequent relative- oscillations of the land and 

 water levels. The close association of igneous rocks with them, some 

 at least of which seem only found in this association, is thought to 

 point to closely contemporaneous igneous action on a large scale. 



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