442 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



conglomerates in the Newark deposits between New York and Virginia 

 only on their western margins; the second is the overlap of the eastern 

 border of the Newark in New Jersey by Cretaceous sediments, showing 

 that at this time the eastern barrier was very low and in places submerged. 



The movements recorded in the Paleozoic eastern border lands of 

 North America south of the Saint Lawrence evidently were not uniform 

 in the two parts separated by the latitude of New York City. In the 

 New England part vulcanism played an important role. Not so much 

 in the south, where, moreover, there is little reason to believe that Paleo- 

 zoic sediments occur beneath the Mesozoic and Tertiary deposits of the 

 Coastal Plain like those found in the eastern part of New England, 

 Following the general strike of the rocks, folding would seem to have 

 taken place in the strip just east of the ^^great fault" (Saint Lawrence 

 and Hudson rivers) at an earlier date than in the apparently corre- 

 sponding bend south of New York. Probably, as has been suggested by 

 Willis and others. New England exposes marginal parts of the conti- 

 nent, the structural equivalents of which are submerged beneath the 

 waters of the Atlantic or covered by the blanket of later deposits forming 

 the southern Coastal Plain. However, the more or less metamorphosed 

 character of the rocks north of New York City and east of the great 

 fault, and certain extraordinary features concerning the distribution 

 of particular faunas and sediments in this area, suggest a supplementary 

 explanation, namely, if the evidence in hand were fully discussed, I 

 believe it might be shown with a fair degree of plausibility that over- 

 thrusting has progressed to such an extent in western New England, 

 eastern New York, and southern Quebec that bands corresponding in 

 original geographic position to the Ordovician slates in east central 

 Virginia have been brought into juxtaposition with bands corresponding 

 in original strike to the Appalachian Valley troughs. 



Overthrust troughs in eastern New Yorh and western New England. — 

 I believe that in the area between the Adirondacks and the Hudson Eiver 

 on the west and the Green Mountains and Berkshire Hills on the east 

 the outcrops of varying types of rock represent deposits in originally 

 distinct troughs that have since been thrust westward over each other. 

 Irregularities in thrusting, and in subsequent as well as concomitant 

 erosion, are responsible for the present outcrops of the buried troughs. 

 The evidence on which this belief in distinct troughs is based is three- 

 fold in character, faunal, lithologic, and structural. The first is shown 

 by differences in fossil contents, the deposits in the Chazy basin just to 

 the east of the Adirondack mass being filled with associations of organic 



