CLASSIFICATION OF THF MISSISSIPPIAN SERIES 313 



between the Great Basin and the interior provinces was sub- 

 merged, allowing the incursion of the Great Basin fauna with 

 its persistent Devonian species into the interior. This recurrent 

 Devonian element in the faunas of the interior, first definitely 

 recognized in the Spring Creek limestone from near Batesville, 

 Ark., 1 is the faunal mark of the initiation of a new chapter in 

 the geologic history of the continental interior. This element 

 is characteristic of the St. Louis fauna wherever it exists. One 

 of the best known of the St. Louis limestone faunas is that of 

 the Spergen Hill beds in Indiana, and in this fauna the recur- 

 rent Devonian element is recognizable in the species of Micro- 

 don, Co?iocardiu7n and Nuculana, genera which had disappeared 

 from the interior of the continent during the Osage epoch. 

 Although the Spring Creek and Spergen Hill faunas are quite 

 different in many minor details, they possess many species in 

 common, showing their relationship. .In addition to this resem- 

 blance of the Spergen Hill fauna to the Spring Creek fauna, 

 which is closely allied to the Great Basin fauna, a fauna prac- 

 tically identical with that of the Spergen Hill beds has been 

 recorded from the far northwest in Idaho, 2 an occurrence which 

 suggests the possibility of its immigration into the interior from 

 that direction. 



During the latter part of the Osage epoch there was appar- 

 ently an emergence of the northern shore line in the region of 

 Iowa, because the younger beds of the Osage group do not 

 extend so far north as the older ones. With the beginning of 

 the Ste. Genevieve epoch, however, this was all submerged 

 asfain, and the St. Louis limestone strata extended farther to the 

 north than the immediately preceding ones. This submergence 

 was followed by a considerable reelevation at the north, the 

 Kaskaskia beds being deposited only in the southern portion of 

 the province. The successive changes, more or less abrupt, in 

 the sediments of the Ste. Genevieve group from limestone to 

 sandstone, to shale and back again to limestone, etc., indicate 



1 Am. Jour. Sci., XLIX, p. 94. 

 -A.J. S. (3), V, p. 383. 



