30 GREEN MOUNTAINS IN MASSACHUSETTS. 



tain system as far as the Connecticut valley, there is a series of schists 

 having a great aggregate thickness. Prof. Emerson, to whose report the 

 reader is referred for the descriptions and for the views of our predecessors, 

 lias been able to divide these schists into several distinct formations with 

 persistently defined characters and boundaries. Above the nonfeldspathic 

 Rowe schists comes a horizon of hornblende schist (Chester amphibolite) 

 often with serpentine, varying from a feather edge to 3,000 feet in thick- 

 ness, overlain by over 9,000 feet of "upper hydroniica-schist" (Plainfield 

 schist). This in turn is overlain by the "Calciferous mica-schist" of the 

 Vermont survey (Conway schist), which obtained its former name from the 

 presence of occasional large lenses of more or less biotitic limestone, which 

 latter has beds of hornblende-feldspar-schist in places along its bottom and 

 top. Above this again is the heavy bed of Leyden argillite, with inter- 

 calated quartz-schist. Next above and unconformablv superposed are the 

 representatives of the Devonian. The age of these different formations 

 still remains uncertain, though at least the Leyden argillite and the Conway 

 schist ("Calciferous mica-schist") are supposed by Prof. Emerson to belong 

 to the Upper Silurian. 



While the Green mountain system includes the whole region between 

 the Connecticut and the Hudson, its characteristic features consist, as we 

 have seen, of the central anticlinal ridge of the Green mountains proper 

 on the east, the synclinal range of the Taconic mountains on the west, and 

 a succession of high, synclinal, island-like masses rising from the intermedi- 

 ate valley. The results of the survey in northwestern Massachusetts lead 

 to the supposition that the central or main ridge was in pre-Cambrian time 

 outlined as a mountain range of highly crystalline rocks on the western 

 border of an area of dry land. During long exposure to the action of 

 atmospheric agencies and of the products of vegetable decay, the rocks of 

 this region had become decomposed at the surface and disintegrated at 

 depths. 



The breaching action along the advancing shore line of the Cambrian sea 

 found ready prepared the materials which the water assorted and distributed 

 t< > f< inn the great sheet < if Cambrian rocks. While these deposits of detritus 

 were accumulating over the shallow areas, the materials for the future lime- 

 stone were gathering offshore to the west. As the positive movement 



