Author Description

This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1921 edition. Excerpt:...the southeast corner of Shackelford County, the western half of Eastland and Brown counties, the eastern half of Callahan and Coleman counties to the southwest corner of McCulloch County, as shown in Figure 13. Lithologic Character.--The Cisco group consists of a series of sandstones, shales, and limestones and several thin coal seams. Most of the sandstones are confined to the lower portion of the section and to the Figure 14. Block diagram showing the thickening of the basal portion of the Cisco group in the northern part of the Pennsylvanian area stones containing lenses of gravel. The shales are more calcareous, lighter colored, and thinner than the shales of the older formations, and here and there may be seen in the weathered slopes tints of red, yellow, and purple, bright colors which are rarely seen in the beds of the Canyon group. Also some of the shale beds of the Cisco are very fossiliferous. The limestones are much thinner and more ferruginous and more crystalline than those below, and most of them are very persistent and make excellent horizon markers for determining structural relationships. Topography.--The Cisco group of formations gives rise to a very different topography from that of the Canyon group below or the Wichita group above. There are no high, sharply defined cliffs, deep canyons, and rough, angular hills. The relief is smaller and the topographical lines have gentler curves. In travelling east and west, east-facing scarps of less altitude than those of the Canyon group alternate with singular regularity with long, gently westward-dipping, mesquite-covered slopes, wit hhere and there sandstone-capped hills sustaining a growth of black-jack oak intervening to break the monotony. Divisions.--The Cisco group has...