294 R. T. Hill—Cross Timbers in Northern Texas. 
diverse as those concerning their origin. Dr. 8. B. Buckley, 
in his “ First Annual Report of the Agricultural and Geologi- 
cal Survey of the State of Texas,’’ erroneously calls the lower 
member the “upper” (p. 61) in one place, and refers them to 
the ‘‘ Miocene,” and on the next page he speaks of them both 
as probably “Tertiary.” Messrs. Blake and Hitchcock, on 
their geological map of the United States (1876), delineate only 
the lower member of the Cross Timbers, and color it Hocene. 
Mr. A. R. Roessler’s series of county maps of Texas represent 
the upper timbers as Tertiary. A prominent authority on the 
Southern States Tertiaries, in a private letter, maintains that 
the upper member is Carboniferous, and the lower one of the 
Cretaceous period (Ripley). Dr. R. H. Loughridge, in the val- 
uable treatise so often mentioned in this paper, gives the best 
account of them that I have seen in print, and calls them 
“stratified Quaternary drift.” Mr. W. J. McGee, naturally 
accepting Dr. Loughridge’s theory as the most plausible, incor- 
porated it in his Map of the United States, accompanying the 
Fifth Annual Report of the Director of the U. S. Geological 
Survey, Washington, D. C., 1886.* 
With all of these theories in mind, I must confess that I 
visited the region this summer with a preconceived idea that 
I should find some one of them approximately true, and I 
was greatly surprised to find them all equally erronéous. 
Topographic and geologic characteristics. 
Before a proper appreciation of the relations of the two mem- 
bers of the Cross Timbers to each other can be arrived at, it is 
necessary to briefly review the salient topographical features of 
this portion of the State of Texas.t The river drainage of the 
State indicates the only general feature in its topography—a 
slope of the surface from northwest to southeast; but even to 
this feature there are several important exceptions. For my 
own convenience I have divided the topographic features of 
the State into the following broad areas: 
First.—The Coast Plain, a continuation of the topographic 
features of the Gulf States so far as they represent old outlines 
of Post-Cretaceous sedimentation of the Gulf of Mexico. 
Although a portion of the Cretaceous strata for a short distance 
west of it could be classified geologically with this Coast plain, 
its topographic border is made to coincide with the interior 
border of the marine Tertiary, the plain being mostly a forest- 
covered section of country, and at a much lower altitude than 
the prairie region. 
Second.—The “ Black Prairie Region.”” This constitutes an 
elongated, triangular region continuing from Arkansas and 
* Mr. C. H. Hitchcock also accepts this in his late map, 1886. + See map. 
