GEOLOGY OF THE LAKE PLACID QUADRANGLE 6/ 



A brief summary of the writer's views may be stated as 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 conse- 

 quent tendency toward parallel arrangement of intrusives and 

 invaded Grenville masses; the foliation is essentially a flow-struc- 

 ture produced by magmatic currents under moderate pressure dur- 

 ing the intrusions ; the sharp variations of strike on large and small 

 scales, and rapid variations in degree of foliation, are essentially 

 the result of varying magmatic currents under differentiated 

 pressure, principally during a late stage of magma consolidation; 

 the almost universal, but varied, granulation of these rocks was 

 produced mostly by movements in the partially solidified magma, 

 and possibly to some extent by moderate pressure after complete 

 consolidation; and the mineral flattening or elongation was caused 

 by crystallization under differential pressure in the cooling magma. 

 It would seem, therefore, that the general absence of foliation 

 from so much of the Marcy anorthosite is best explained as the 

 result of much more uniform intrusion of this single great body 

 which was probably a stiffer or less fluid magma and which is less 

 involved with Grenville masses, or, in other words, to much less 

 forced differential flowage. 



Foliation of the gabbro and gabbro-diorite. As already stated, 

 the interior portions of most of the gabbro bodies are nonfoliated 

 and they possess a diabasic texture, while the outer portions are 

 highly foliated rocks, often true amphibolites. In many places the 

 degree of foliation varies considerably within single stocks. More 

 or less granulation is very common. This foliation and granulation 

 have been quite generally regarded as secondary features produced 

 by severe regional compression. But it is very diflicult to imagine 

 a process of development of foliation, which boxes the compass 

 around the borders of the gabbro masses, by regional compression. 

 Such foliation often of course strikes directly across the foliation 

 of the older adjacent rocks. If due essentially to regional com- 

 pression of the solidified gabbro, should not the foliation every- 

 where strike at least approximately at right angles to the direction 

 of application of the pressure? Also how are such notable varia- 

 tions in foliation and granulation to be explained? 



According to the writer's view, the foliation and granulation of 

 the gabbro stocks are largely, if not wholly, primary features due 

 to movements in the magma before final consolidation. Consider- 

 able pressures must have obtained within the stock chambers while 



