File:Annual report of the United States Geological Survey to the Secretary of the Interior (1899) (14761103244).jpg

Identifier: annualreportofun2171geol (find matches)
Title: Annual report of the United States Geological Survey to the Secretary of the Interior
Year: 1880 (1880s)
Authors: Geological Survey (U.S.)
Subjects: Geological Survey (U.S.) Geology Water-supply Forest reserves Mines and mineral resources
Publisher: Washington : G.P.O.
Contributing Library: University of Illinois Urbana-Champaign
Digitizing Sponsor: University of Illinois Urbana-Champaign

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dis-tinguishable. South of the San Gabriel the Edwards grades into theoverlying Georgetown formation along the Colorado region, fromwhich it is not separable except by paleontologic criteria. It is truethat the Georgetown limestone is slightly more arenaceous than theEdwards, but the differences are so slight that it requires the trainedeye of the geologist to detect them. As the overlying Georgetownformation in this region is less than 75 feet thick, the layman or welldriller unversed in paleontology can nearly always be sure thatany rock occurring 75 feet below the Del Rio clays belongs to thecombined Comanche Peak and Edwards formations. The eastern parting of the Edwards has not been traced fromOglesby in eastern Coryell County north to the Brazos. Near Oglesbythe Eort Worth limestone is faulted down against the eastern marginof the Edwards. To the north it is overlapped by the Kiamitia claysof the Washita division. On Coon Creek, a short tributary of the Brazos north of Greenock,
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f of ILLINOIS HILL.) STRATIGRAPHY OF THE EDWARDS LIMESTONE. 231 Bosque County, the contact between the massive fossiliferous Edwardslimestone and the Kiamitia cla)r may be seen where Capri mi <mx-sifibra and Requienia forms mingle with Gryplma corrugata of theKiamitia clays. The occurrence of the rudistes and requienias ceasesat the Kiamitia chvys. OCCURRENCE AND DISTRIBUTION. The Edwards limestone within the Grand Prairie north of the Colo-rado occurs in remnantal patches throughout the region between theBrazos and the Colorado. These occurrences are different in aspecteast and west of the Balcones fault line. On the downthrown side of the main fault line which runs just westof Austin, Rounclrock, Georgetown, Belton, and McGregor, the upperstrata are exposed in a narrow belt (which has been previously alludedto). This belt is also sheared by secondary faults on the east and isseldom more than 5 miles wide. Geographically this belt is the innermargin of the Black Prairie region. Th

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