M.iibut.l 480 [March r,, 
the wi(K' lowland conslituliiio- the (loo.l-plaiii of the Mississip))! 
River and on its western side by a somewhat similar lowland iK'lt, 
along which White River and some of its principal tributaries 
flow. The lowland on the east separates the ridge from the 
Tertiary uplands of western Kentucky, Tennessee, and north- 
western Mississippi. The width of the flood-plain varies from 20 
to 40 miles. The lowland on the west separates the ridge from 
the Palaeozoic uj)lands of Arkansas and Missouri by a distance 
varying from 5 to 40 miles. 
From Helena northward^ to the 8t. Francois River the ridge is 
broader and higher than anywhere else, the highest part being 
along the western side which here has an elevation of a little 
more than 200 feet above the flood-plain of the Mississippi River. 
From the crest the western side descends abruptly to the 
lowland and the eastern side slopes gradually eastward to the 
top of the bluff overlooking the Mississippi River floo(l-i)lain and 
then descends abruptly. 
North of the St. Francois River the ridge is l)roken up into 
many small ridges which approach much nearer to the Palaeozoic 
highlands than further southward, thus making the lowland west 
of the ridge much narrower. 
Figure 1 is a diagrammatic representation of the northern |)art 
of the Mississippi embayment. C'rowley's Ridge is shown as a 
heavy dark line. The shoreward limit of the Palaeozoic uplands 
running around the embayment is indicated l)y a dotted line 
running northeastward west of Crowley's Ridge, crossing the 
Mississippi River near Cape Cirardeau, Missouri, and extending 
eastward and then southeastward beyond the Tennessee. 
The prominence of the ridge, a very narrow belt of upland 
in a wide area of very low and flat country, has attracted much 
attention and various hypotheses have been advanced to explain 
its existence. Three of these will be noticed here. 
The first is that advanced by Dr. John C. Branner, state 
geologist of Arkansas, who supposes that the ridge is a residual 
of the coastal plain left as an upland by the erosion of the mate- 
rial from all around it by the Mississippi and Ohio Rivers. He 
'The lucls conceriiiiij;- Crowley's Kid^e were obtuineil mainly from I'rof. It. E. 
Cull's report on that area. Annual rept. geol. surv. of Ark., for 1S8'J, v. J. 
