SIXTH REPORT OF THE DIRECTOR I9O9 147 



b Lake Michigan and Lake Huron. Their location and form 

 correspond to the Michigan basin, where they roughly follow the 

 Devonic belts. 



c Lake Erie and Lake Ontario, either depressions originating 

 from the action of the Atlantic tangential pressure, or counterparts 

 of later warpings in the upper Ohio basin and western New York. 



We have thus far left out of consideration the Appalachian 

 basin or " geosyncline '' which occupies a narrow strip on the 

 west side of Appalachia [chart IV] and is continued northward 

 through New York and Vermont into Canada. It has later 

 become the site of the Appalachian folds. Ulrich and Schuch- 

 ert ^ have clearly shown that this basin became early subdi- 

 vided by longitudinal and transverse barriers into a number of 

 smaller basins. In their directions these barriers foreshadow the 

 later, more intensive Appalachian folding, and are early indications 

 of the influence of the pressure acting from the Atlantic basin upon 

 and through Appalachia. It is certain that the Appalachian basin 

 itself which became the site of the intense folding resulted from 

 the Atlantic pressure upon Appalachia, due to suboceanic spread. 

 It is therefore a foreign element, so to say, in the geologic history 

 of the Palezoic platform which, however, has strongly obscured the 

 original symmetry of the latter. While all changes here noted 

 on the platform are of epeirogenic character, the Appalachian folds 

 are an orogenic feature. 



While in general the isles have emerged in Paleozoic times 

 and the basins have been submerged, there have been continuous 

 changes in the amount of emergence and submergence. This fact 

 becomes especially manifest through Professor Schuchert's paleo- 

 geographic maps, as far as they have appeared in print, and it 

 is probable that these subsidences and elevations took place in 

 rhythmic pulsations. 



With all these continuous changes, however, the sum total of 

 the elevations of isle Wisconsin, isle Adirondack, Ozarkia and 

 Appalachia has been greater than that of the depressions and 

 they represent, therefore, positive elements of the continent in 

 the sense used by Willis ^ while the depressions are negative 

 elements in which, however, in some zones, as in the Cincinnati 

 uplift, the algebraic sum of the unconformities and sediments 

 may approach zero. The most conspicuous negative element 

 is the Appalachian basin with its immense sedimentation. 



' N. Y. State Mus. Bui. 52. 1901. p. 633. 



'Willis, Bailey. Geol. Soc. Am. Bui. 1907. 18:389. 



