PALEOGEOGRAPHIC CONCLUSIONS 465 



appears, to have been in the Atlantic of that cla}^ and the connection could 

 only have been in the Saint Lawrence region, since the facies of the early 

 Upper Devonic deposits to the south, in Maryland and Virginia, changes 

 to black muds, which indicates estuarine conditions, and the dwarfed 

 fauna of which indicates low salinity of the waters. These same estuarine 

 muds which embraced the lower end of the Sherburne Bar seem to have 

 been instrumental in preventing the Hamilton fauna from migrating 

 around the lower end of that bar into the central New York basin. The 

 relation of the bar and the currents which distributed the muds in the 

 estuary seem to have been such as to cause the chief mass of these muds 

 to be spread to the west of the Sherburne Bar. Here they constitute the 

 Genesee, West Eiver, and Middlesex shales, all of which thin away west- 

 ward and northward from south central New York. 



It is quite clear that the changes which brought about the separation 

 of the central New York and eastern basin by the Sherburne Bar, and 

 which inaugurated the deposition of the black muds on the south and 

 the more or less oxidized continental Oneonta sands and muds on the- 

 western slopes of Appalachia, also resulted in the separation of the lowan 

 and New York areas, but only after the final immigration of the Cuboides 

 fauna. From Buffalo westward through Ontario, Michigan, Ohio, In- 

 diana, Illinois, Wisconsin, and Iowa, as well as throughout most of the 

 Eocky Mountain region, dry land conditions came into existence after 

 the deposition of the Hamilton Traverse formation; for everywhere we 

 find the Hamilton-Traverse or, in its absence, the older formations suc- 

 ceeded by an erosion interval, there being everywhere a marked discon- 

 formity between the Middle and Upper Devonic beds. This discon- 

 formity probably extends to the shores of James Bay, where in the Abitibi 

 Eiver Savage and Van Tuyl found shales with a Chemung fauna 

 (Liorhynchus mesaco stalls and. L. glohuliforme) resting upon Traverse- 

 beds.^^ It is quite probable, however, that in the far northwestern region 

 (northwest Canada and Colorado) the deposition was continuous from 

 Middle into Upper Devonic time, and it was here that the Traverse types 

 largely persisted into the Upper Devonic. 



In the central New York region, deposition after the separation of the 

 basins began with the Tully limestones. This lime mud, as I have else- 

 where shown,2« was probably derived from a series of reefs which existed 

 north of the line of' present-day outcrop of the limestone and which have 



33 Communication to the Geological Society of America, Albany meeting, December 

 1916. 



3« Stratigraphic relationships of the Tully limestone and the Genesee shale in eastern. 

 North America. Bull. Geol. Soc. Am., vol. 28, 1917, pp. 945-958. 



