THE MISSISSIPPIAN PERIOD. 505 



thickness of which is about 1500 feet), in eastern Wyoming x (Guernsey 

 and part of the Hartville formation), and in South Dakota 2 (Engle- 

 wood and Pahasapa limestone). A section for this region, is given 

 on p. 554. 



In Indian Territory there was some disturbance at about the 

 close of the Mississippian. The beds warped upward (relatively) at 

 this time suffered erosion, and an extensive chert-conglomerate, the 

 conditions for which were prepared by the interval of erosion, marks 

 the early stage of Carboniferous proper (Pennsylvanian) deposition. 



West of the Great Plains. 



West of the Great Plains the Lower Carboniferous is so widely 

 distributed as to show that the present mountain region as far west 

 as the 117th meridian was mostly submerged, though there were numer- 

 ous islands, 3 some of which occupied the position of existing mountain 

 cores. North of the United States, marine conditions prevailed east 

 of the Gold Ranges, and again west of those mountains. In gen- 

 eral, submergence seems to have been more wide-spread in the west in 

 this period than in the Pennsylvanian period which follows; but in 

 Wyoming submergence was more general in the later period. 4 



The several stages of the epoch, as defined in the Mississippi basin, 

 have not been separately recognized in the west, and, except for the 

 removal (by sinking or otherwise) of the barriers which bounded the 

 Great Basin on the east, it is not known that geographic changes of 

 importance occurred in that region during the progress of the period. 

 Much of the Mississippian system in the west is limestone, though 

 clastic formations are not wanting. 5 The Mississippian formations 



1 W. S. T. Smith and Darton, Hartville, Wyo., folio, U. S. Geol. Surv. As classified 

 in this folio, there is an unconformity in the Mississippian, but conformity between 

 it and the Carboniferous proper. 



2 Darton, 21st Ann. Rept., U. S. Geol. Surv., Pt. IV, p. 503. 



3 Emmons, Bull. Geol. Soc. Am., Vol. I, pp. 263-7. 



4 Knight, Bull. 45, Wyo. Exp. Station, 1900. 



5 The Mississippian is not differentiated from the Pennsylvanian on the maps of 

 most of the western folios of the U. S. Geol. Surv., though the two are sometimes 

 differentiated in the text. The Carboniferous (Mississippian and Pennsylvanian) 

 is shown in the following folios of the west: Colorado, Anthracite and Crested Butte, 

 Pike's Peak, Ten Mile District and Walsenburg; Wyoming, Absaroka, Yellowstone and 

 Hartville; Montana, Fort Benton, Little Belt, Three Forks and Livingston; Utah, 

 Tintic; Arizona, Bisbee; and on most of the California folios. 



