iS95-J 479 [Marbut. 
The occurrence of Permian and earlier Mesozoic strata in the 
west wouhl indicate the presence of a sea basin in that direction 
into whicli the drainage of the upper Mississippi valley could 
escape, thereby obviating any necessity for escape southward. 
During Cretaceous time the peneplain was submerged on its 
southern side and received a cover of Cretaceous sediments 
which are known up the Mississipjji embay ment nearly to Cairo. 
As evidence is wanting that the Cretaceous sediments ever had 
a much wider extent than is indicated by the present form of 
the embayment we may infer that the i)eneplain was warped at 
the time of submergence and that the form of the Mississippi 
etnbayment was given early in Cretaceous tnnes. Having in 
this way introduced the ocean level to the vicinity of Cairo and 
having the head of the embayment surromided by a peneplain 
surface warped with a gentle slope toward the emba^mient, it is 
an easy step to consider either that the drainage of the u})per 
Mississippi basin was turned into the embayment as a result of 
the warping or that a stream working backward from the head 
of the embayment captured the interior drainage. 
In this way a rational explanation is given for the occurrence 
of the lower Missi.ssip[)i in its present jjosition, and while it is 
not possible to adopt the explaruition as a comjjlete demonstra- 
tion, yet it is jnuch su|)erior to an assumption that the river 
has been where it is now, since the close of the Appalachian 
revolution. 
THE GEOGRAPHIC DEVELOPMENT OF CROWLEY'S 
RIDGE. 
BV ('. F. MARIiUT. 
Crowley's Ridge is a long, narrow belt of upland, lying within 
a large area of lowland in northeastern Arkansas and south- 
eastern Missouri. It extends in a slightly crescentic form from 
the Mississippi River near Cape Gu'ardeau, Missouri, southwest- 
ward to Helena, Arkansas. It is limited on its eastern side bv 
