I48 NEW YORK STATE MUSEUM 



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 passed. 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 Central basin 

 was divided by a secondary peninsula (Kankakee) and Ozarkia 

 joined to a vast western tract. But at the same time the two 

 arms of the platform with their northern isles Wisconsin and 

 Adirondack (as peninsulas) and the southern land bodies of 

 Ozarkia and Appalachia remained distinct elements and like- 

 wise the Mediterranean basin remained defined in its general 

 outline. 



The main outlets from the Paleozoic [see chart III] passed 

 eastward between the 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 River formations do 

 not cross the connecting Frontenac axis. The St Lawrence de- 

 pression, however, frequently became an important highway of 

 migration (as in Beekmantown, Onondaga and Hamilton times) 

 through its southward connection, by different straits, at dif- 

 ferent times with depressions between the Isle Adirondack and 

 Appalachia [see p. e. Schuchert's map of Onondaga time]. 



There are facts available that indicate approximately the time 

 when the symmetric arrangement of the Paleozoic platform took 

 place. As we have noted before, Algonkian sedimentation took 

 place around Lake Superior [see chart I] but aside from this some- 

 what independent depression, the whole platform was, according to 

 Walcott's investigations, 1 above sea level until Upper Cambric time, 

 with the exception of the Appalachian geosyncline. The relation' of 

 the Upper Cambric deposits to the Isles Wisconsin and Adirondack 

 would indicate that in this period the separation of the Paleozoic 

 eastern basin and of the inclosing arms, took place and prob- 

 ably also the beginning of the breaking up of the arms. The 

 Isles Wisconsin and Adirondack, Ozarkia and Appalachia have 



l See pi. 2, 3 of Walcott, U. S. Geol. Sur. Bui. 81, 1891. 



