32 GREEN MOUNTAINS IN MASSACHUSETTS. 



coarser material to have been laid down, during the positive movement, over 

 the gneiss area. In the subsequent folding I imagine that the rigidity of 

 the unaltered granitoid mass offered far greater resistance to the folding 

 than any of the superposed material, and that, as a result of this resisting, 

 inverted wedge, the material of the eastern limb was subjected to the slip- 

 ping or shearing movement producing the coarse laminated structure of 

 these gneissoid rocks, while the similar material on the west limb, having 

 a more rigid base which yielded less readily to overfolding, was forced into 

 minor overfolded crumples and crushed into a finer grain. Beneath the 

 gneisses remade out of the conglomerate by dynamic action during the 

 folding, there would be formed more or less similar transitional rocks 

 through the action of the same dynamic processes upon the semidisinte- 

 grated surface of the older rock. This is what is found at many points 

 along this contact in Hoosac mountain. 



From what has just been said it is evident that the high degree of 

 metamorphism of the Paleozoic rocks is intimately connected with the 

 folding. It is also a salient fact that, while the schists and limestone are 

 wholly recrystallized throughout the whole folded area beginning west of 

 the Taconic range, the change of the underlying < lambrian quartzite to 

 a crystalline rock — a white gneiss — does not begin until, in going east, we 

 reach the central, main range. In this sense the metamorphism of the 

 schists is regional; that of the quartzite has the appearance of being local. 



Both the quartzite and the overlying schists contain tourmaline, crys- 

 tallized in situ, and frequent lenses or faulted veins of quartz, feldspar, and 

 tourmaline. The schists contain in places needles of rutile. As we follow 

 the quartzite in its transition to white gneiss we find here and there peg- 

 matite veins, more often near its contact with the core of older gneiss. 



If we could go back to the original character of the sediments we would 

 find west of the western flank of Hoosac mountain a column of fine sedi- 

 ments, probably argillaceous, with, in places, calcareous bands, resting on a 

 thousand feet or more of limestone, and this on six or eight hundred feet 

 of Lower Cambrian grit — here a quart/, sandstone. On the eastern side of 

 the western flank of Hoosac mountain we would find mam- thousand feet 

 of the same fine sediments resting on, and passing downward into the 

 Cambrian grit — here a coarse conglomerate abounding in detrital feldspar 



