GENEEAL STEUCTUEE AiSIl) COEEELATION. 25 



along- the west side and south end of the mountain, and it is not impossible 

 that it may be accompanied there, as here, by the same rupture. If this is 

 so, then the position of this overthrust plane would lie above and to the east 

 of the schist trough shown on the Buttress (PI. in, c, u). 



Having sketched thus briefly the general relation of the crystalline 

 schists of the main ridge of the Green mountains to the fossiliferous rocks 

 lying to the -west, let us now return to the main ridge. 



We have seen that the Cambrian white gneiss rests with a time break on 

 the coarse granitoid gneiss In places on Clarksburg mountain we find the 

 micaceous quartzite more or less conglomeratic at the base, resting on the 

 granitoid gneiss, the two rocks sharply distinct. In others, as on Hoosac 

 mountain, a conglomerate rests on the granitoid gneiss with sharp definition. 

 But this simplicity is not always present, especially at the meeting of the 

 white and granitoid gneisses. In general there intervenes between the 

 well-defined coarse gneiss and the well-marked white gneiss a zone of beds 

 of more or less coarse gneiss, often alternating with finer grained biotite 

 schists. It is not easy in such places to draw the line between the Cam- 

 brian and pre-Cambrian formations, though, as I will show further on, in 

 some instances there is good reason to draw the line at the base of the 

 transitional beds where these show alternating strata of varying character. 

 One thing appears certain : the dynamic action which has folded these rocks 

 has impressed upon them not only their cleavage and plication, but also the 

 remarkable* simulation of conformity in bedding and of vertical transition. 



The pre-Cambrian core of the Green mountains reappears at frequent 

 points along the range. In places it forms almost island-like masses of old, 

 hard gneisses surrounded by the Cambrian quartzites and allied rocks, as 

 in the northwestern corner of Connecticut. In others, as on Hoosac and 

 Clarksburg mountains, it appears as limited, oval, dome-like areas of granitoid 

 gneiss. Again, as in Chittenden, Vermont, it consists of a long, narrow 

 line of coarse gneiss, at eroded points in the backbone of the range. 

 Finally, as between Clarendon and Ludlow, in Vermont, where the height 

 of the range has been cut down by the removal of the younger rocks, the 

 core of the folded range shows itself in a variety of old granitic and 

 gneissoid rocks, cut by intrusives and with extremely irregular structure 



