Marbut.] 482 [March 6, 
Another liypotliesis is tliat ailvaiu^o.l by IVof. li. E. Call, 
formerly assistant geoloi'-ist on the Arkansas geological survey. 
He supposes that, at the time of the u])lift of the Atlantic, and 
Gulf coastal shelf into the present coastal plain, the Mississippi 
River separated into at least two distributary brandies at 
the head of the embayment, one of which flowed southward, 
west of what is now Crowley's llidge, excavating the lowland 
belt on its western side, and the other flowed more dii-ectly 
southward along the present course of the Mississippi Iliver. 
Subsequently the valley west of the ridge was al)andoned and 
that part of the river joined the other, forming the modern 
Mississippi. 
The other hypothesis is that of the writer who supposes, with 
the others, that Crowley's Ridge is a residual of the coastal plain 
sediments left in relief by erosion of material from all sides of it, 
but differs from the others in supposing that the lowland belt 
lying along the western side of the ridge is a subsequent lowland, 
worn on weak rocks by the streams now flowing in it, and that 
the only work that has been done directly by the Mississippi 
River is the excavation of the valley along the eastern side of 
the ridge. 
In order to show the reasons foi- tliis explanation it will be 
necessary to call attention to some of the features, in tlie matuie 
stage, of the topographic development of a coastal plain. 
(^11 the uplift of a, part of the continental shelf into a coastal 
]ilain, of the Atlantic or Gulf coast type, the rivers di-aining the 
old land and formerly entering the sea at the inner margin of 
the c(»astal plain will be extended across the latter to its present 
shore line as new consequent streams. The rocks making up the 
coastal lAii'm will be composed of strata of varying resistance to 
erosion dii)ping gently seaward. If the slope of the surface 
raised above sea level be greater than the grade of the largest 
streams extended across it, as is usually the case, the first work 
done upon it will be a channehng of its surface. The larger 
streams will soon cut their channels down to grade. In doing 
so they will encounter certaiji harder strata of the coastal plain, 
but the largest of the streams will not be greatly delayed by 
them. The smaller streams, however, will be greatly retarded, 
