28 The American Geologist. Jan. \m 
small amount of surface water which is not imbibed by the 
soil, is found in a few and widely distributed ponds. Its 
eastern and northern edges are incised by deep and vertical 
canons of streams which are cutting by backward or head- 
water erosion. Two streams flow across or around the plains, 
but in origin they are probably antecedent thereto, as will be 
shown later. These are the Canadian and the Pecos. Neither 
of them receives any of the surface drainage of the plain. The 
rainfall, principally from June to September, is from 20 to 25 
inches (estimated). 
The surface of the plain is everywhere composed of the rich 
transported sedimentary soil which I have recently described 
as the Staked Plains formation,''' and which is from 100 to 
300 feet deep. From its structure and composition it is 
evident that it is either a lacustral or alluvial deposit, laid 
down in late Tertiary or early Quaternary times. The forma- 
tion and its resultant soil differs from all others in Texas, and 
notwithstanding the deficient rainfall, the plains are rapidly 
being settled by an industrious population. 
Upon every side, with the slight exceptions above mentioned, 
the plain is surrounded by majestic scarps, which afford splen- 
did vertical sections of the structure and the stratigraphy. 
These scarps are very irregular upon the eastern edge, and are 
marked by many deep, almost vertical canons,'" such as Canon 
Blanco, which is about nine hundred feet in depth. Eastward 
prolongations of these plains extend down the principal drain- 
age divides, and probably were once continuous across the 
present denuded region to the Grand Prairie, as is still the 
case with the divide of the Pecos and the Colorado. The 
northern and western scarps — those of the Canadian and the 
Pecos respectively— are more regular and less jagged. It is 
not appropriate at the present time to enter into a discussion 
of the age or detail of this structure, but it is sufficient to say 
that in these scarps at various places can be seen a grand 
sequence or strata, from the palaeozoic rocks at the base of its 
southwestern corner, the Red Beds formations above them, the 
Grand Prairie formations above these, and surmounting the 
whole, the peculiar formation of transported loam, gravel and 
other soil which constitutes everywhere the summit of the 
1^ American Ass. Adv. of Science, Toronto meeting, 1889. 
