Geology . ckbeds of limestone (or chalk) occur in other parts of the series. In thevicinity of the shores, especially next to the Ouachita uplift, wherethe shore phases of the formation are best known, the formation isrelatively thin and mainly clastic. The Fredericksburg series ismuch less variable, both in thickness and composition, than the Trinityseries below, and contains more calcareous material. The Fredericksburg formation is overlain by the Washita, a serieswhich records an epoch of shoaling waters, though the sea was some- 1 Hill, op. cit., p. 129 et seq. 2 Idem. 3 Eldridge, Bull. 21
Geology . ckbeds of limestone (or chalk) occur in other parts of the series. In thevicinity of the shores, especially next to the Ouachita uplift, wherethe shore phases of the formation are best known, the formation isrelatively thin and mainly clastic. The Fredericksburg series ismuch less variable, both in thickness and composition, than the Trinityseries below, and contains more calcareous material. The Fredericksburg formation is overlain by the Washita, a serieswhich records an epoch of shoaling waters, though the sea was some- 1 Hill, op. cit., p. 129 et seq. 2 Idem. 3 Eldridge, Bull. 213 U. S. 6eol. Surv., p. 301. THE COMANCHEAN PERIOD. 117 times clear enough to allow of the accumulation of impure limestone. Theseries is made up of alternating beds of clay, limestone, sandstone, its typical development in Texas, more than half the Comancheansystem is calcareous, and chalk, rather than limestone in its ordinaryform, prevails. In general, the clastic beds thicken toward the Ouachita. Fig. 382.—Shows the effects of faulting on outcrops of the various Cretaceous for-mations, near Uvalde, Texas. Ce (Edwards limestone), Cdr (Del Rio clay),and Cb (Buda limestone) are the local subdivisions of the Comanche systemKef (Eagle lord foimation) is the lower part of the (Upper) Cretaceous. Mountains, while the beds of chalk, which point to clearer water, thickenin the opposite direction. Locally the Comanchean system of Texasis deformed and notably faulted (Figs. 381 and 382). Westward and northward extension. — The Comanchean forma-tions originally spread westward from Texas over a considerablearea in eastern New Mexico, and probably even to Arizona, where thesystem is 5000 feet thick1 and carries the Texan fauna,2 and north- 1 Ransome, Professional Paper 21, and Bisbee folio U. S. Geol. Surv. Stanton, Professional Paper 21, U. S. Ceol. Surv., p. 70. US GEOLOGY. wnnl around fche western end of the Ouachita Mountains, an undeter-mined distance into Thoug
Size: 1703px × 1466px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectgeology
