108 NEW YORK STATE MUSEUM 



General Conclusions 



The writer believes that the evidence of ' intense folding of the 

 Grenville by the action of strong orogenic forces throughout the 

 northwestern Adirondacks is conclusive. On the one hand, a portion 

 of the evidence derived from a study of the metamorphism of the 

 syenite-granite complex conforms with this. On the other hand, 

 the evidence points equally strongly to the primary origin of the 

 foliation accompanied by a wave of crushing which swept in from 

 the outer border and died away as it advanced. The correlation of 

 these two apparently opposed theories necessitates a very close 

 synchronism between the mountain-building forces and the intrusion 

 of the entire syenite-granite complex. These conclusions parallel 

 those reached by McMahon 1 in his work in India. There the igneous 

 rocks were intruded during the 'time of action of orogenic forces 

 which folded and crumpled the strata of the Himalayas and their 

 gneissic structure was induced in them before complete solidification. 



From the external structures and internal textures of the rocks 

 of the syenite-granite gneiss complex, we may infer that we are 

 dealing with a heterogeneous magma which was intruded in two or 

 more stages under the influence of a cycle of orogenic compression. 

 Thus the primary banding or belting of the rocks is a feature which 

 took its origin during the process of intrusion and represents facies 

 of different composition which have been squeezed out into these 

 elongated lenses by compressive forces. Although the primary 

 banding and foliation were thus controlled by the action of lateral 

 compressive forces, the latter were inefficient in crushing the min- 

 erals crystallizing out from the magma until they had become so 

 abundant as to interfere and form an open crystal meshwork. This 

 was not until after the intrusion of the satellitic dikes and veins 

 such as the hyperites, pegmatites etc., and after the feldspars and 

 other minerals had already formed large phenocrysts in the magma, 

 with only a small amount of interstitial liquid material rema'ning. 

 These inferences are indicated by the facts that the dike rocks have 

 suffered the same degree of metamorphism as their inclosing rocks, 

 and that large crystals of feldspar, augite and hornblende are still 

 more or less abundant as the uncrushed eyes of augen in the rocks 

 of the Diana mass. The orientation of these in alignment parallel 

 to the primary banding which is in diverse directions suggests, 

 however, that the crystals were oriented to a considerable extent 



1 McMahon, C. A., " Granite of the Himalayas," Geol. Magazine, I 



p. 212-20. 



