THE MISSISSIPPIAN PERIOD. 503 



The peculiar fauna! changes which resulted from the geographic 

 changes referred to are discussed elsewhere (p. 518). Suffice it here 

 to say that the fauna of the St. Louis limestone of the Mississippi River 

 region contains species which seem to have lived in the region which 

 is now the Great Basin, but to have been unable to escape from it, 

 at least to the eastward, until this time. Their escape and migration 

 to the eastward at this time is the reason for believing that the barrier 

 which had heretofore restricted them was broken down. 



It was perhaps during this epoch that the Bedford limestone of 

 Indiana, famous as a building stone, was deposited. Much of this 

 limestone is foraminiferal, and was long mistaken for oolite. It 

 is in the beds of this epoch, too, that many of the great limestone 

 caves of Kentucky and southern Indiana occur. 



In Michigan conditions seem to have remained much as before 

 for beds containing salt (brine) and gypsum (Michigan series) were 

 still in process of deposition, 1 at least during the earlier part of this 

 epoch. 



The strata east of the Cincinnati arch have not been definitely 

 correlated with those of the third stage of the period farther west. The 

 limestone-making conditions of the Mississippi River region may have 

 extended eastward, south of the Cincinnati arch, to eastern Kentucky, 

 Tennessee, and West Virginia. Farther north the sediments of this 

 stage were predominantly clastic, and constitute the upper portion 

 of the Waverly series. Locally, deposits of this time contain both 

 coal and iron ore. 2 In the northern part of the Appalachians the 

 Mauch Chunk shales 3 were in process of deposition, while other names 

 (Pennington, Canaan, 4 etc.) are applied to the contemporaneous 

 deposits farther south in the same mountain system. The Mauch 

 Chunk shales contain some iron ore. 



The Kaskaskia (Chester) beds. — The fourth stage of the Mississippian 

 period, according to the classification adopted for the Mississippi 

 basin, seems to have been marked by more restricted waters and more 

 varied sedimentation, for sandstone and shale are sometimes asso- 

 ciated with the limestone of this epoch. The deposits of this stage 



^eol. Surv. of Michigan, Vol. VII, Pt. II, pp. 13-15. 



2 Geol. Surv. of Ohio, Vol. Ill, p. 819. 



3 The name Mauch Chunk is applied as far south as Maryland; see Jour, of GeoL 

 Vol. IX, pp. 422-4. 



4 See Tennessee folios. 



