﻿102 NEW YORK STATE MUSEUM 



margins of the bathylith, and hence boxes the compass in direc- 

 tion. At the same time the rock of the bathylith, while solidify- 

 ing, may develop a similar and parallel foliation. 



While it can not be affirmed that such results were not brought 

 about in the region, it can be positively stated that, if so, they 

 have been so disguised by subsequent compressive stresses that 

 the effects of the two can not now be successfully disentangled. 

 This is shown in several ways: (a) the microscopic study of the 

 granite gneiss indicates that, to a considerable extent at least, 

 its foliation is due to recrystallization rather than to original 

 crystallization, in other words the rock has been much crushed 

 and somewhat recrystallized under compressive stress, since it 

 originally congealed; (&) these later stresses seem to have been 

 severe enough to materially change the shape of the bathylithic 

 masses, elongating them greatly in the northeast-southwest direction 

 and correspondingly pinching them together in the direction at right 

 angles to this; (c) instead of the foliation running around the 

 bathyliths, with parallelism to the margin, it retains its general 

 northeast-southwest strike throughout the region, independendently 

 of these margins, so that either no such marginal foliation was 

 ever developed, or else it has been practically eliminated by the 

 subsequent compression ; (d) later igneous rocks than the granite 

 gneiss have also had a foliation developed as a result of com- 

 pression, most prominently in the earlier ones, and with steady 

 decrease in prominence in the later. 



It thus appears most probable that the general parallelism of 

 the foliation of all the Precambric rocks, and its substantial uni- 

 formity in direction throughout the region, is chiefly owing to 

 compression of later date than that of the Laurentian granite in- 

 trusion. This appears increasingly true in going eastward into, 

 and across, the Adirondack region. The rocks show steady in- 

 crease in amount of metamorphism, in degree of mashing and re- 

 crystallization, in uniformity of foliation, and in obliteration of 

 such possible structures as primary foliation. Some of this in- 

 crease may be ascribable to greater thickness of cover, but the 

 evidence of thoroughgoing compression of much later date than 

 the Laurentian, is very clear. 



Foliation of the later igneous rocks. The Alexandria and 

 Theresa syenites seem closest to the Laurentian in age, among 

 the conspicuous igneous rocks of the district. The Alexandria 

 syenite shows cores of fairly massive rock, not foliated though 

 with a considerable amount of crushing. But the porphyritic 



