EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA 157 



bergian and the quartzites above with distorted brachiopods are Oriskany, 

 is as close an approximation to the truth as the known facts permit. 



We must now again call attention to the attitude of the Helderbergian 

 and Oriskanian rocks in the Helderberg mountains of New York, reiter- 

 ating the statement made on the first page of this memoir. They stand in 

 an escarpment facing the west, north and east overlain by the great thick- 

 ness of later Devonic and Devono-Carbonic constituting the Catskill moun- 

 tains. Their faces are terraced faces of erosion. Their former extent was 

 in the directions which they face. Beyond any doubt these rocks extended 

 eastward of the Hudson and into western Massachusetts. In the view of 

 Prof. B. K. Emerson, the ultimate authority on the crystallines of Massa- 

 chusetts, there was here in western Massachusetts an undoubted Precambric 

 north-south ridge whose position above water is indicated by the presence of 

 a Cambric quartzite fringing the greater portion of the outcrops. This may 

 have been repeatedly depressed and elevated and the adjoining Siluric 

 masses brought to day but there are no antagonistic considerations for 

 assuming that it was all transgressed during the Devonic and these 

 Devonic deposits removed entirely by erosion. Toward the north of this 

 region near the north line of the state is a break in the Precambric ridge 

 which is of considerable width, extending into Vermont and this may have 

 well served as a passage for Devonic sediment from New York into the Con- 

 necticut trough. East of the Connecticut river there is only a limited area 

 of Precambric near the Rhode Island line, extending south into Connecticut 

 along Long Island sound. This is everywhere margined by a quartzite 

 interpreted as Cambric, and this with the fossil-bearing Cambric localities 

 at Nahant, North Attlebury and Braintree was raised into land and so 

 continued through Siluric and Devonic time, no rocks of this age being 

 determinable. Professor Emerson regards all these rocks above the Cam- 

 bric as Carbonic coextensive with the Worcester and Mansfield coals. 



These conclusions give evidence enough of an old land barrier bound- 

 ing a trough of Devonic waters in which the metamorphosed beds of Ber- 

 nardston at least were deposited. The rest may have been removed by 



