604 INDEX TO THE STEATIGRAPHY OF NORTH AMERICA. 



The beds of the Washita division in general are more varied in composition, of greater 

 thickness, and more closely resemble shallow-water deposits toward the northern border region, 

 extensive formations of ferruginous sands and bituminous clays occurring in that direction, 

 which cease to the south. In general the strata of the Washita division, as a whole, become 

 more calcareous to the south, but even this rule has its exceptions. 



As a whole, the group decreases from about 400 feet in the Denison section on Red River 

 to less than 175 feet in the Austin section, on the Colorado. This loss in thickness of the Washita 

 division to the south is compensated for by a corresponding gain in that direction in the thick- 

 ness of the Edwards limestone of the Fredericksburg division, so that the thickness of the 

 Comanche series in its entirety is not impaired thereby. 



The individual indurated beds of the Washita division seldom exceed a foot or two in 

 thickness. The strata rarely extend through a hundred vertical feet without conspicuous 

 lithologic or faunal changes. These individual beds are remarkably persistent in horizontal 

 extension, especially when they are studied in large local areas, preserving their lithologic and 

 paleontologic characters without any perceptible change for great distances. When the beds 

 are traced through long distances, such as Texas provides, gradual important changes may be 

 noted which can be appreciated only by comparison of widely separated minute local sections. 

 What is a conspicuous clay formation in the Red River section may become a limestone when 

 traced 300 miles south to the Colorado, or a formation which is a limestone upon Red River 

 may be a clay on the Colorado. 



Owing to these gradual changes in the character of the rocks the sections of the Washita 

 division at the extreme ends of the area treated in this paper, as exemplified in the Denison and 

 Austin sections, present entirely different lithological aspects and sequences, the relations of 

 which would not be traceable were it not for the existence of certain well-deternained paleon- 

 tologic zones which persist regardless of the lithologic changes. 



The Washita division presents several well-defined mappable units— eight, for instance, 

 along Red River, and only three at Austin, on the Colorado. 



In the region of its typical development as seen in the Red River section there are eight 

 broad subdivisions: (1) Basement beds of bituminous clays rather abruptly succeeding ■ the 

 Edwards limestone; (2) beds of white, arenaceous, chalky limestone alternating with marls, 

 which terminate with (3) a conspicuous limestone formation; (4) a group of beds of marls and 

 shell conglomerates; (5 and 6) two groups of clays and sands separated by limestone; (7) an 

 upper limestone; and (8) an uppermost lime marl. 



These subdivisions, which are locally still further subdivided into conspicuous beds, may 

 be named the Kiamitia, Duck Creek, Fort Worth, Denton, Weno, PaAv-jjaw, Main Street, and 

 Grayson beds. To the south, in the Colorado sections, only three lithologic members are 

 recognizable — the Georgetown limestone, Del Rio clays, and Buda limestones. Each of these 

 formations, although possessing very marked and important features in particular localities, 

 loses its identity when traced through long distances, by coalescing with other formations. 



I 14-15. NORTHERN TEXAS, SOUTHERN OKLAHOMA AND ARKANSAS, AND NORTHERN 



LOUISIANA. 



Of the Lower Cretaceous of this region Veatch *'**'' writes as follows: 



The lowest Cretaceous beds represent the near-shore deposits of the sea advanciag over 

 the old Jurassic peneplain and are, therefore, sandy and contain vegetable remaias, as well as 

 brackish-water shells. These are succeeded by limestone and marls, indicating deeper water, 

 and these in turn are limited above by the great sand beds that represent the extreme shallow- 

 water conditions which marked the beginning of the upper Cretaceous. 



In Arkansas only the lowest of the series, the Trinity sand, is well developed, although 

 near the Indian Territory line are good outcrops of the Goodland limestone, overlain by a 

 series of marl and limestone beds, which, with the Goodland limestone, represent the other 

 two grand divisions of the Comanche series, the Fredericksburg and the Washita. 



