646 THE JOURNAL OF GEOLOGY. 



GEOGRAPHIC CONDITIONS ACCOMPANYING THE DEPOSITION OF 

 PALEOZOIC SEDIMENTS IN THE CORDILLERAN SEA. 



The assumed area of the Cordilleran or Paleo-Rocky mountain 

 sea includes over 400,000 square miles between the 35th and 55th 

 parallels. To the eastward during lower and middle Cambrian 

 time a land area is thought to have extended from east of the 

 1 1 ith meridian across the continent to the Paleo-Appalachian 

 sea. This land was depressed toward the close of middle Cam- 

 brian time, and the Mississippian sea expanded over the wide 

 plateau-like interior region, from the Gulf of Mexico on the 

 south to the Lake Superior region on the north ; westward it 

 penetrated among the mountain ridges between the 105th and 

 1 1 ith meridians, laying down the upper Cambrian deposits that 

 are now found in New Mexico, Arizona, eastern Utah, the west- 

 ern half of Colorado, Wyoming, Idaho and Montana, and still 

 farther north into Alberta and British Columbia. During Ordo- 

 vician, Silurian, Devonian, and Carboniferous time this entire 

 Mississippian region, except portions in Devonian time, appears 

 to have been covered by a relatively shallow sea that was co-ex- 

 tensive with the Appalachian sea and that communicated freely 

 with the Cordilleran sea. During this same age, however, the 

 Rocky mountain area of New Mexico, Colorado, Utah, Wyom- 

 ing and Montana formed a more or less well-defined boundary 

 of ridges and islands between the Cordilleran and the interior sea 

 up to the 49th parallel. To the north of the latter the condi- 

 tions appear to have been the same as on the eastern side of the 

 continent, where the Appalachian sea communicated freely with 

 the Mississippian sea. From the data that we now have I think 

 that the Paleozoic (Mississippian) sea extended at times over 

 nearly all of the area subsequently covered by the Cretaceous 

 and the later formations between the Gulf of Mexico and the 

 Arctic ocean. This belt is bounded almost continuously on the 

 east and west by Paleozoic rocks that extend from the Arctic 

 ocean to Mexico, and whether of Cambrian, Ordovician, Silurian 

 or Devonian age they carry essentially the same fauna through- 

 out their extent. In the outcrops of lower strata that rise up 



