THE OROGENIC EPOCHS IN NORTH AMERICA 641 



The tract within which the rocks were crumpled during this 

 epoch stretches from western Newfoundland through Cape Bre- 

 ton Island, Nova Scotia, New Brunswick, Maine, and probably 

 southern New England, and was wide enough to include on the 

 northwest the Gaspe Peninsula in eastern Quebec. Farther south- 

 westward, the evidence becomes scanty, but the marked uncon- 

 formity beneath the basal Carboniferous beds near Boston and in 

 Rhode Island suggests that it extended at least as far as Long Island 

 Sound. Willis' has shown that the great thickness of late Devo- 

 nian and early Carboniferous clastic rocks in Maryland and Virginia 

 strongly suggests the rise of mountain ranges immediately to the 

 east, in the region now occupied by New Jersey and eastern 

 Virginia. Using the same criterion, the dwindling and eventual 

 disappearance of such formations between Virginia and Alabama 

 suggest that the folding did not extend the entire length of the 

 present Appalachian Mountain belt. 



Although there are some discrepancies in the evidence and hence 

 some disagreement among writers on the subject, the testimony of 

 unconformities on the one hand, and of thick clastic formations on 

 the other, indicates that the Brunswickian disturbance culminated 

 after the middle of the Devonian but considerably before the close. 

 In Acadia the folds had been truncated before the Lower Carbon- 

 iferous (Mississippian) period and beds of that age were deposited 

 upon the eroded stubs. 



Arkansan {mid-Pennsylvanian) . — -The folded structures under- 

 lying the mountains of Arkansas and Oklahoma were made, as 

 nearly as can be inferred from current correlations, in the latter 

 part of the Pennsylvanian period. Thus in the central Arkansas 

 coal field the deformation followed the laying-down of the lower 

 Pennsylvanian coal measures,^ but no younger strata exist there. 

 In the Arbuckle Mountains of Oklahoma it occurred after the 

 deposition of the Caney shale (early Pennsylvanian ?) and before 

 that of the Franks conglomerate (late Pennsylvanian). In the 

 Wichita Mountains still farther west in the same state, the folds had 

 been truncated before the deposition of the Oklahomian (early 



^ Bailey Willis, Geol. of Maryland, IV (1902), 23-93. 



= A. J. Collier, "Coal Fields of Arkansas," U.S. Geol. Survey, Bull. 326, p. 24. 



