IXTRODLTTIOX. 



an undotprmincd distanco southward and an 

 interval of omorgcnce, followL-d by a rapid 

 transgression of the shallow Midway sea ap- 

 proximately to the. limits of the Ripley sea. 

 The waters of the Midwaj' sea, however, ap- 

 pear to have been deeper and the transgres- 

 sion falls somewhat short of reaching the Rip- 

 ley shore line except at the head of the Missis- 

 sippi Gulf in southern Illinois and in the vicin- 

 ity of Little Rock, Ark. At the ch)se of tiie 

 Midwa}- most of the area again became land, 



a> will l)e shown in the subsequent discussion 

 of tlu' Wdcox group. At the maximum of the 

 Wilcox transgression, whicii followed this pe- 

 riod of emergence, most of this area was again 

 submerged, but the whole upper part of the 

 cmbayment was a region of lagoons and shift- 

 ing sands with littorsil and piUustriiie deposits, 

 marine faunas not having been found north of 

 l!ititud<> .33°, while the deposits of Wilcox age 

 extend to latitude 37° at least. 



