GEOLOGY OF THE LUZERNE QUADRANGLE 43 



gree of foliation, are essentially the result of varying magmatic 

 currents under differential pressure, principally during a late stage 

 of magma consolidation ; the almost universal but varied granula- 

 tion of these rocks was produced mostly by movements in the 

 pattially solidified magma, and possibly to some extent by moderate 

 pressure after the complete consolidation; and the mineral flatten- 

 ing or elongation was caused by crystallization under conditions of 

 differential pressure in the cooling magma. 



Structure of the Gabbro and Metagabbro 



It is believed that the old gabbros exhibit foliation due to two 

 separate and distinct causes. Foliation is not uncommon well 

 within the gabbro masses, especially the larger ones. Both the 

 degree and direction of such foliation vary notably within short 

 distances, even within single bodies, a good example being in the 

 area i^^ miles northwest of Stony Creek village. Such foliation 

 is considered to be largely, if not wholly, a primary feature due to 

 magmatic movements or differential flowage while the magma was 

 being intruded under deep-seated conditions. 



Portions of borders of many of the gabbro bodies, and many of 

 the smaller ones as a whole, are more or less foliated amphibolites 

 which are commonly finer grained and more granulated than the 

 usual gabbro. Such amphibolites are believed to represent gabbros 

 which have been subjected to pressure of the enveloping syenite- 

 granite magma with resultant development of this second type of 

 foliation. 



Many of the gabbro bodies, especially the smaller ones, show a 

 strong tendency to be arranged with their long axes parallel to the 

 foliation of the inclosing syenite or granite. Such masses may be 

 regarded as inclusions which tended to swing into parallelism with 

 currents of the great bodies of the intruding syenite-granite magma. 



Structure of the Mixed Rocks 



All the mixed rocks of the quadrangle are more or less foliated, 

 and most of them are distinctly banded. As a glance at the geo- 

 logic map will show, the strike and dip of such foliation and band- 

 ing are almost invariably the same as those of the adjacent granite 

 or syenite. In some cases igneous rock dips under the mixed rocks, 

 while in other cases the mixed rocks dip under the igneous rock. 

 Bodies of mixed rocks may lie within the igneous rock, or bodies 



