172 C. SCHUCHERT THE NORTH AMERICAN GEOSYNCLINES 



two confluent geosynclines, with at times very dissimilar developments 

 stratigraphicallj;, fannally, and even orogenetically. For these reasons 

 the term Appalachian geosyncline, in the restricted sense, will refer to 

 the trough south of Vermont, while to the one northeastward of Massa- 

 chusetts we will apply the term Saint Lawrence sea, made familiar to us 

 by the Canadian geologists and James D. Dana. It should be remem- 

 bered, however, that there appears to be no sharp geographic boundary 

 between them. Furthermore, both troughs during Lower and Middle 

 Cambrian times appear to have spread either confluently or singly across 

 Xew Jersey and the southern New England States into the Atlantic 

 Ocean (Poseidon). From Upper Cambrian time into the Devonian the 

 two geosynclines were structurally more or less confluent, though their 

 seas were at times not continuous. On the other hand, the Saint Law- 

 rence geos^Ticline often brought into the interior seas of America parts 

 of north European faunas, while the Appalachian one continued into the 

 Antillean mediterranean, having south European and South American 

 faunal connections. 



RESTRICTED APPALACHIAN GE08TNCLINE 



The sedimentary history of the actual Appalachian geosyncline con- 

 tinued from the beginning of Cambrian to the close of Pennsylvanian 

 time, and it was a far more persistent, longer enduring, and more deeply 

 subsiding trough than the Saint Lawrence geosyncline. Then, too, this 

 periodically subsiding trough was more often filled with variably exten- 

 sive shallow seas, and these at times were continuous with the waters of 

 the Saint Lawrence geosyncline. Previous to the Middle Silurian, the 

 ^Appalachian seas often spread widely also into the Mississippian sea, but 

 after the completion of the Cincinnati arch the floods were restricted to 

 the eastward of this geanticline. 



The Appalachian trough was more or less completely drained of its 

 marine waters at least Sight times (Middle Cambrian, close of Beekman- 

 town, close of Ordovician, Guelph, close of Silurian, late Devonian, and 

 twice during the Mississippian). It is certain, however, that locally it 

 was dry far more often than eight times, but this matter can be made 

 plain only through a detailed statement of the history of the trough, and 

 this is not the occasion to present the succession of paleogeographies. 



Sedimentation in the Appalachian geosyncline was by no means con- 

 tinuous nor uniform in the rate of deposition. The Cambrian and Ordo- 

 vician are in best development south of Pennsylvania, while the Devonian 

 is almost restricted to north of Tennessee. The Cambrian and Ordo- 



