42 NEW YORK STATE MUSEUM 



zontal strata under load of much overlying material. In other 

 words, it was static metamorphism possibly aided by heat of the 

 great volumes of slowly rising magmas. According to this view 

 the parallelism of foliation and stratification would normally have 

 developed. 



Structure of the Syenite-granite Series 



The various facies of the syenite-granite series seldom fail to 

 exhibit at least a faint foliation. They are very commonly clearly 

 foliated, and locally excessively so. The degree of foliation varies 

 notably even within short distances. Both strike and dip also vary 

 notably, as shown on the geologic map. There is really no con- 

 spicuously general trend or strike of foliation throughout the quad- 

 rangle, but rather locally, over areas of a few square miles, both 

 strike and direction of dip may maintain considerable uniformity. 



The foliation is usually accentuated by the roughly parallel 

 arrangement of dark minerals, though locally the granite, where it 

 is comparatively free from dark minerals, is strikingly gneissoid 

 due to extreme flattening of feldspar and quartz. Examples of 

 highly foliated facies are given in the description of the syenite- 

 granite series. Granulation of minerals, especially feldspar, is com- 

 mon in many places and often highly developed. 



For a long time the foliation of the Adirondack syenite-granite 

 series has been ascribed to severe compression brought to bear upon 

 the region after the great intrusions. But the lack of anything like 

 a persistent strike of the foliation, and the evidence against notable 

 regional folding of the Grenville strata, led the writer some years 

 ago^^ to regard the foliated syenite and granite to be essentially 

 " primary gneisses " whose gneissoid structure developed as a sort 

 of magmatic flow-structure under conditions of moderate com- 

 pression rather than by severe lateral (orogenic) pressure brought 

 to bear upon the region after cooling of the magmas. Briefly 

 stated, the writer's explanation follows. During the processes of 

 intrusion, which were long continued, the great magmatic masses 

 were under only enough lateral pressure to control the general 

 strike of the uprising magmas with consequent tendency toward 

 parallel arrangement of intrusives and invaded Grenville; the folia- 

 tion is essentially a flow-structure produced by magmatic currents 

 under moderate pressure during the intrusions ; the sharp variations 

 of strike on large and small scales, and the rapid variations in de- 



"Jour. Geol., 24, 1916. p. 600-16. 



