SIXTH REPORT OF THE DIRECTOR I909 1 43 



has transgressed it, and the eastern one by the submergence of 

 portions southeast of the Adirondacks and by extensive fold- 

 ing. In their original position the two arms may be conceived 

 as approaching- each other somewhat in the south, although not 

 nearly so much as they do now, in consequence of the forcing 

 inward of the eastern arm, for if the considerable shortening 

 of the Eastern basin indicated by the Appalachian folds, is taken 

 into account and the basin spread out to its original width, the 

 eastern arm would probably take a position fully corresponding 

 to that of the western. 



These two arms bound a large basin [B of chart II], the 

 *' Paleozoic eastern basin," now occupied by the basin of Ohio and 

 the Great Lakes. In the middle of this an elongated low eleva- 

 tion formed, now indicated by the Cincinnati and Nashville " up- 

 lift." 



The axial position of this uplift [see line Bo-B;^ on chart I] 

 suggests that it may partake of the nature of the '' geanitidinal 

 median " ^ that according to Haug ^ forms along the median line 

 of a geosyncline preparatory to more extensive folding. The 

 southern portion of the uplift which according to its normal posi- 

 tion to the basin and the Precambric arms, should extend due 

 south, has been affected by the Appalachian folding and twisted 

 into a southwest direction. As a result of the warping of the 

 axis of the basin, two separate symmetric basins have been 

 formed,^ one, the Eastern Interior, and the other, the East Cen- 

 tral basin. On account of the approach of the Precambric arms 

 in the south, these basins do not extend north and sofuth, but extend 

 symmetrically to northwest and northeast. The Ohio river from 

 the Pennsylvania to the West Virginia line flows along the axis 

 of the eastern basin. 



The northern portion of the Paleozoic platform that lies to the 

 north of the Cincinnati geanticline assumed the aspect of a separate 

 subcircular basin, typically indicated by the Michigan coal field 

 and the locations of Lake Michigan and Lake Huron. It also 



^ Dana clearly recognized this uplift as a geanticline. 



2 Haug, £mile. Soc. Geol. Fr. Bui. 28, ser. 3. 1900. p. 617, and id. 

 Traite de Geologic I. 1907. p. 164. 



'Dana [Areas of Continental Progress in North America, etc., Geol. 

 Soc. Am. Bui. 1890. 1:41], recognizing the importance of the regions 

 of shallow seas represented by the Cincinnati uplift and the Precambric 

 region of Missouri as regards rock-making, has distinguished these 

 basins by the terms here used. 



