. Annual report of the United States Geological Survey to the Secretary of the Interior . section(fig. 1; see also PI. II, B).These rocks occur as strata ofdifferent hardness, tilted atsteep angles in the mountainousareas, and nearly horizontal inthe plains region (see fig. 11).They are of two general classes,differing in occurrence and rela-ative importance, viz: 1. An older or fundamentalseries of pre-Cretaceous forma-tions. The stiuctural arrange-ment of these formations, inanticlines and synclines, is dis-cordant with that of the laterformations of the CoastwardSlope. The series represents
. Annual report of the United States Geological Survey to the Secretary of the Interior . section(fig. 1; see also PI. II, B).These rocks occur as strata ofdifferent hardness, tilted atsteep angles in the mountainousareas, and nearly horizontal inthe plains region (see fig. 11).They are of two general classes,differing in occurrence and rela-ative importance, viz: 1. An older or fundamentalseries of pre-Cretaceous forma-tions. The stiuctural arrange-ment of these formations, inanticlines and synclines, is dis-cordant with that of the laterformations of the CoastwardSlope. The series representsthe remains of an ancienttopography which was base-leveled during Jurassic andCretaceous time, prior to theinvasion of the Cretaceousseas, which completely buriedit with later sediments. Theseolder rocks, except in themountains, are now seen only5 where areas of the later stratafig. ideologic formations of Texas. have been worn away. In the structure of this group is written an interesting pre-Cretaceous history, Silurian: .. ] RELIEF OF THE PALEOZOIC ROCKS. 33 involving the growth and decay of relief features quite different indetail from those of the present time, which is described more fullyin later pages. 2. Formations of the-Coastward Slope, from Cretaceous to Recentage. Most of these rocks were once marginal deposits of the Gulf ofMexico, laid down when it extended much farther inland than it doesto-day; and as they were elevated the Gulf receded from the RockyMountains front to its present position. All these strata now inclinetoward the sea. In some instances the inclination coincides with thesurface slope, while in otheis it is slightly greater. Relief expression of the older or Paleozoic sedimentaries.—Classifiedaccording to geographic importance the older rocks may be dividedinto two groups—the earlier and the Inter Paleozoic. The first includesthe Algonkian and Cambro-Ordovieian; the second, the Carboniferous,with the Permian. They may
Size: 985px × 2538px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1800, booksubjectgeology, booksubjectwatersupply
