410 Rucdemann — Sipnmetric Arrangement in the 



cpcin)s);eiiic character, the Appalachian folds are an orocjenic 

 foaturo. 



While iu general the isles have emerged in Paleozoic times 

 and the hasins have been submerged, there have been contin- 

 uous changes in the amount of emergence and submergence. 

 This fact becomes especially manifest through Pi-ofessor 

 Schuchort''s paleogeographic maps,* and it is ])robable 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,t while the depressions are negative 

 elements in which, however, in some zones, as in the Cincin- 

 nati uplift, the algebraic sum of the unconformities and sedi- 

 ments may approach zei'o. The most conspicuous negative 

 element is the Appalachian basin with its immense sedimenta- 

 tion. 



The symmetry of arrangement of the platform is likewise 

 but a surplus of symmetric features in the general structure 

 over many asymmetric details in the different stages through 

 which the platform has jjassed. This again is well shown by 

 the charts of Professor Schuchert. It will be seen that at 

 times the Nashville uplift was joined to Appalachia, and the 

 Eastern Interior basin moved northward, while the East Cen- 

 tral basin was divided by a secondary peninsula (Kankakee) 

 and Ozarkia joined to a vast western tract. But at the same 

 time the two arras of the platform with their northern isles 

 Wisconsin and Adirondack (as peninsulas) and the southern 

 land bodies of Ozarkia and Appalachia remained distinct ele- 

 ments, and likewise the Mediterranean-like basin remained 

 defined in its general outline. 



The main outlets from the Paleozoic sea (see fig. 2) passed 

 eastward between Isle Adirondack and Appalachia and 

 westward between Isle Wisconsin and the Ozark uplift and 

 southward between Ozarkia and Appalachia. The Wisconsin 

 and Adirondack isles have apparently been frequently attached 

 to the protaxis. This becomes especially manifest in the case 

 of the Adirondack isle, where the Beekmantown, Pamelia, 

 Chazy, Lowville and probably also Black Piver formations do 

 not cross the connecting Frontenac axis. The St. Lawrence 

 depression, however, frequently became an important highway 

 of migration (as in Beekmantown, Onondaga and Hamilton 

 times) through its southward connection, by different straits, at 

 different times with depressions between the Isle Adirondack 

 and Appalachia (see^. e. Schuchert's map of Onondaga time). 



* Bull. Geol. Soc. Amer., xx, 427-606, 1910. 



•I- Willis, Bailey, Bull. Geol. Soc. Amer., xviii, 389, 1907. 



