28 GREEN MOUNTAINS IX MASSACHUSETTS. 



inward the same structure is similarly defined in the granitoid gneiss and 

 is perfectly conformable in the two rocks, although we have here, in the 

 conglomeratic character of the base of the quartzite and in the pre-Cambrian 

 erosion of the Stamford dike, evidence of a time-break. If we imagine the 

 granitoid gneiss to have been deeply disintegrated and to have been abraded 

 only to the semidisintegrated zone, or even to the lower zone in which 

 only the integrity of the micaceous element had been attacked, then the 

 material of this zone would have presented itself to the force that produced 

 the crinkling and lamination in much the same physical condition as the 

 sand and pebbles of the quartzite. 



Again, take the coarse gneisses with blue quartz which occur at many 

 points along the core. Mr. Wolff finds them to contain the same feldspar 

 with the same inclusions as that of the granitoid gneiss, except that they are 

 light colored, while those of the granitoid are reddish, and they have fre- 

 quently the same blue quartz. But they are bedded and have alternating 

 layers of finer schists, and appear as transitions conformable to the under- 

 lyiug granitoid and overlying white gneiss or other equivalents of the Cam- 

 brian quartzite. The granitoid gneiss consists of large crystals of feldspar — 

 perhaps averaging one by three-quarters by one-third inch in size— and 

 flattened lenses of blue quartz and thin, irregular layers of mica. I imagine 

 that these materials, taken from the zone of semidisiutegration and quickly 

 deposited, would, in their new arrangement, produce our "transitional 

 coarse gneisses," while the material of the upper zone of complete decay 

 would furnish the sand and clay for the quartzite and finer sediments. 



If this reasoning be correct, we should in many instances include in 

 the Cambrian quartzite series the coarse, more thinly bedded gneisses, with 

 their interbedded, finer grained schists. Hut in the present state of our 

 knowledge of the Green mountains the granitoid gneiss appears to he only 

 one of the constituents of the old core, and perhaps a subordinate one. 

 From our recent work in Vermont it seems that the pre-Cambrian area will 

 be found to contain a variety of granites, gneisses, and schists, as well as 

 basic rocks, which will need to be studied in connection with the rocks of 

 both the New York highlands and the Adirondacks. It therefore remains 

 to be discovered whether the old core contains any rocks of the periods be- 



