AREAL GEOGRAPHY OF NORTH AMERICA IN THE LATE PALEOZOIC 255 



of Canada, and Prince Edward Island, was made up of isolated and semi- 

 isolated troughs of varying size, outlined by the pre-Pennsylvanian surface. 

 The whole outline of this area and the general trend of the individual 

 troughs indicate a contour parallel to the older elevations of western New 

 England and of this portion of Canada and to the (probable) western edge 

 of Appalachia. The distinct character of this area is indicated not only by 

 the shape of the troughs and the different character of the deposits, depen- 

 dent largely upon the small size and isolation of the troughs, but upon the 

 difficulty in correlating the deposits with those of the larger basin to the 

 southwest. The continuation of the northeastern area to the south beyond 

 the coast of Rhode Island is strongly suggested and leads to the impression 

 that a depression existed in the surface of Appalachia which continued 

 south for an unknown distance, entirely east of the present exposed edge 

 of that old land. If this be true, Pennsylvanian deposits must lie buried 

 beneath the coastal waters of the Atlantic and the deposits of the Atlantic 

 Coastal Plain. The presence of such a depression, even if confined only to 

 the northern part of Appalachia, would have an important bearing upon the 

 explanation of the different character of the sediments in the Northeastern 

 and the Southern Subprovinces. 



The southern basin was far larger than the northeastern. It extended 

 from the western edge of Appalachia far into Ohio and Kentucky and at 

 its largest reached into Indiana and Illinois. As has been repeatedly 

 shown, the basin was contracting from originally very wide limits through 

 all Pennsylvanian time, until in the Conemaugh and Monongahela it was 

 restricted to western Pennsylvania and West Virginia and eastern Ohio 

 and Kentucky. The portion west of the Cincinnati anticline, originally 

 connected with the eastern part, was in late Pennsylvanian time receiving 

 deposits as a completely or partially isolated area. In middle Conemaugh 

 time came the first effects of the uplift of the eastern side of North America ; 

 the eastern part of the basin continued sinking under the accumulating 

 load of sediments, but the western part was gradually raised into the zone 

 of erosion and purely terrestrial deposition. 



The elevation of eastern North America, the initiation of Permo-Carbon- 

 iferous conditions, produced very different effects in the two subprovinces. 



The first deposits of the northeastern basin are coarse conglomerates — 

 the lower conglomerates of Prince Edward Island, the New Glasgow con- 

 glomerate, the Roxbury conglomerate, and the Dighton conglomerate. 

 A part of these, the Squantum tillite member of the Roxbury conglomerate, 

 is of glacial origin, and glacial conditions lingered for some time, as is shown 

 by the series of advances and retreats of the ice demonstrated by Mansfield.^ 



1 The author is as fully aware of the uncertainty of the stratigraphic position of the deposits 

 in the Boston Basin as his readers will be, but believes that the similarity of conditions 

 there to those of deposits of determined stratigraphic position to the north and south is 

 a bit of confirmatory evidence of their Permo-Carboniferous age worthy of consideration. 



