DEVONIAN AND MISSISSIPPIAN FAUNAS 279 
more or less inclosed Appalachian Basin east of the Cincinnati island, 
where the Maxville limestone represents the Ste. Genevieve formation 
of the Mississippi Valley. To the southwest, in northern Arkansas, 
the Spring Creek limestone, a formation which, with the Batesville 
sandstone, is essentially contemporaneous with the Ste. Genevieve, 
and probably uncomformable upon the subjacent Osage beds, carries 
a most remarkable fauna with peculiar immigrant forms from the far 
southwest,’ a faunal character which indicates that the Mississippian 
sea reached so far in that direction as to communicate with the Western 
Continental Province, where these peculiar forms had existed, some 
of them having persisted from Devonian time. 
Subsequent to the great extension of the sea during Ste. Genevieve 
time the northern portion of the Mississippi Valley Basin became dry 
land, and so remained until it was reoccupied by the sea in Pennsyl- 
vanian time, with only a partial readvance in early Chester time. In 
the extreme southern portion of Illinois and in Kentucky, Ulrich? has 
recognized three members in the Ste. Genevieve formation, the Fre- 
donia, the Rosiclare, and the Ohara, but in all the region north of 
Chester, Ill., the upper portion is wanting and the superjacent Cypress 
sandstone rests unconformably upon the lower beds of the Ste. Gene- 
vieve. The higher beds of the Ste. Genevieve in the extreme southern 
Illinois, especially the Ohara beds of Ulrich, bear a fauna which has 
much in common with the faunas of the Chester above the Cypress 
sandstone, but even here there is possibly an unconformity between 
these beds and the Cypress. 
The Cypress sandstone initiates the Chester, the closing epoch of 
the Mississippian in the typical portion of the Mississippi Valley 
Basin, during which period the conditions of sedimentation were 
continually shifting, there being interbedded limestone, shale, and 
sandstone formations, the limestone and shale predominating below, 
above the initial Cypress sandstone, and the sandstones being more 
conspicuous above. No remnant of these beds is preserved, so far as 
known, north of a point some miles south of St. Louis, although it is 
possible that the Chester sea extended further north than this. It is 
quite certain, however, that this sea never had the great extent to the 
t Williams, Am. Jour. Sct. (3), XLIX, 94-101. 
2 Professional Paper, U.S. G.S., No. 36, p. 38. 
