Invasion to Regional Metamorphism. 257 



tions of composition from unaltered country rock to pure 

 igneous rock. The penetration of the magma has not 

 been accomplished by the massive invasion of appreciable 

 viscous fluids, but is more suggestive of capillary action 

 and intercrystallization. The thinnest of parallel^ mica 

 laminae may be traced throughout their length without 

 showing such crumpling as even the inertia of the least 

 viscous fluid would have given them if the invading 

 magma had all been fluid. From sheets of magma and 

 of schist which are only of crystal thickness, all grada- 

 tions in width may be traced into wide bands of country 

 rock or equally wide dikes of pegmatite or granite. The 

 phenomena are extensively displayed in Connecticut, and 

 the writer is more particularly familiar with the large 

 field of mixed rock known as the Waterbury gneiss, 

 extending through western Connecticut from Torrington 

 to Derby. Doctor G. 0. Smith and the writer studied 

 this area in 1906, and came to the conclusion that the 

 best way for making field maps was, knowing the pure 

 types of cover rock and granite, to estimate for each 

 outcrop the ratio of the two. This would give data for 

 deciding where, and on what basis, formation boundaries 

 should be drawn. 



[Doctor Fenner-^"^ has described the same features in 

 an independent study of the highlands of New Jersey. 

 He clearly shows that the hydrous magmatic emanations 

 or differentiates may precede the magma lit-par-lit by 

 penetrating small pores where their lower viscosity allows 

 them much more rapid movement than the main magma. 

 This penetration of solutions makes the rock more like 

 magma in composition, as w^ell as conducting magmatic 

 heat in advance of the magmatic invasion, until finally, 

 if the magma advances, it reaches a rock so modified that 

 one would expect it to be readily assimilated.] 



The great bursting power of freezing water is well 

 known, even when acting between surfaces such as joint 

 planes, which permit free ingress and egress to the water. 

 Becker and Day^^ have discussed this power as exhibited 

 by other crystals. The phenomena of f eldspathization, as 

 shown in lit-par-lit structure, suggest that for such mixed 

 gneisses this factor should be elevated to a first place. A 

 solution permeates and passes through a foliated rock. 

 The temperature falls as the solutions flow outward. The 



-' C. N. Fenner, Jour. Geology, 22, 594 and 694, 1914. 



2«G. F. Becker and A. L. Day, Jour. Geology, 24, 313-333, 1916. 



