CORRELATION OF SHAMMATTAWA LIMESTONE 353 



separated localities as the Wyoming, Lake Winnipeg, and Hudson Bay- 

 regions may be seen from the foregoing table. This resemblance extends 

 not only to the specific identity of the more common fossils, but also to 

 the unusual coral associates in this fauna and the peculiar coral elements, 

 as Streptelasma latuscula var. trilohata and an undescribed species of 

 Streptelasma having the convex side flattened. It also includes similar 

 variations in such characteristic brachiopod species as Dinorthis near 

 subquadrata having unusually coarse radiating striae, and a large, coarse 

 form of Rhynchotrema cf. capax. A similar fauna was also found by 

 Walcott in the upper part of the Fremont limestone of Colorado. The 

 similarity in the faunas of this age in the different localities is such as to 

 indicate that the Eichmond strata in the Colorado, Wyoming, Lake Win- 

 nipeg, and Hudson Bay regions were deposited in the same marine prov- 

 ince or basin of deposition, which was doubtless connected at the north 

 with the Arctic Ocean. This fauna is quite different from the more or 

 less contemporaneous fauna of the Maquoketa in the upper Mississippi 

 Valley, or from that of the Eichmond farther east, in Indiana and Ohio. 

 When the meager bryozoa fauna associated with Dinorthis aff. sub- 

 quadrata and Rhynchotrema near capax and other late Cincinnatian fos- 

 sils in the Hudson Bay and Lake Winnipeg regions is compared with the 

 great number and variety of species belonging to this class of fossils in 

 the Maquoketa and Eichmond strata of the Mississippi and Ohio valleys, 

 many of the bryozoa in the latter region belonging to families not repre- 

 sented in the late Cincinnatian fauna of the Hudson Bay region, it seems 

 impossible that the source of the Maquoketa and Eichmond faunas of the 

 eastern and central United States could have been in the north, as has 

 generally been assumed. It is much more probable that the fauna of the 

 Maquoketa and Eichmond of the Mississippi and Ohio valleys were of 

 southern or eastern origin, and that they invaded the interior of North 

 America from the south, as shown on the paleogeographic map, figure 1. 

 On this map, as on those that follow, the lined areas represent the exten- 

 sion of the seas on the continent. 



Silurian Eocks in the Hudson Bay Eegion 



earlier studies 



Exposures of Silurian rocks along Attawapiskat Eiver were mentioned 

 by BelP in 1886, who described the Silurian coral reefs outcropping for 

 33 miles above the head of Lowasky Island. 



b^ 



^ Robert Bell : Report on an exploration of portions of the Attawapiscat and Albany 

 rivers. Geol. Survey of Canada, Summary Rept., 1886, pp. 24G-29G. 



