44
as were worked out in the field or defined by the maps in a striking manner. As a consequence but little of the argument can here be pre- sented, and the most that can be promised is a conscientious effort to divest the facts of any garb of mere personal opinion.
The object of the present report being largely economic, it is mainly devoted to a consideration of the commercial possibilities of the region.
I.—THE GENERAL GEOLOGIC SECTION.
The rocks which lie at surface in the counties immediately bordering the Central Mineral Region are of Lower Cretaceous or Jurassic time. The settlement of the real horizons of the beds must be relegated to the specialists who are still debating the question. It is sufficient for our immediate purpose to warn investors that, in any event, no valua- ble deposit of coal or lignite may be expected within this range, although worthy people have proposed boring to test the matter. All the important lignite layers lie in a geologic position considerably above this. There is much difference, however, in the contacts at the edge of the Central Region in different localities. Upon the east and southeast the Cambrian and Silurian strata are in direct contact with the Jura-Cretaceous; farther westward the Carboniferous, and still farther the Permian rocks, lie directly beneath higher Cretaceous strata, speaking generally, until, in Tom Green county, south of San Angelo, the passage from Permian or Permo-Triassic to Cretaceous is direct, without the intervention of the Jura-Cretaceous. Continuing the section southward to the Rio Grande, successively higher Cretaceous beds are encountered, thickening rapidly and overlapping like shingles upon a roof. The same relations are apparent in higher beds down the Rio Grande from Del Rio to Eagle Pass and across the country from Del Rio to Spofford, although this latter course is more nearly on the strike than on the dip of the strata.
The geologic history of the region under review is very interesting, although its study reveals a different record from what cursory observations would lead one to infer. The evidences which have been mentioned in previous reports by the writer, of shore lines bordering the Central Mineral Region, are as plainly depicted in successively retreating repetitions through the Cretaceous series southward. The gradual thickening of the strata seaward and the overlap at the shore- ward edges, are marked features which cannot be mistaken when checked off at frequent intervals along continuous lines of accurate leveling. This is particularly observable in the course of Devil's river"
It is this very significant fact which has had much to do with the writer's belief that the Central Mineral Region was a land area during a large part of the Cretaceous time. This opinion, however, was formed and announced partly upon other grounds before the work of 1891 had brought to light these facts in all their extent.