598 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



burg fossils, but the faunas of the individual formations have not been collected with sufficient 

 fullness to permit their paleontologic definition. * * * 



The lowermost formation of the Fredericksburg group is composed of calcareous rocks that 

 are well exposed in the Finlay Mountains, where, in the central part of the dome, they he 

 unconformably on the Hueco formation. At the base of the Cretaceous section is a limestone 

 conglomerate about 25 feet thick composed of rounded pebbles of Carboniferous lime- 

 stone averaging possibly about 2 inches in diameter. Above this are 350 feet of gray hmestone, 

 which is generally massive but locally contains nonpersistent, thin-bedded limestone grading 

 into shale. * * * 



The Campagrande formation is conformably overlain by the Cox formation. 



The Cox formation consists of massive soft brownish sandstone, some intercalated gray 

 limestone, and near the base a red-drab shaly member. The formation averages about 600 feet 

 in thickness and is subject to variation in composition, so that no one section is typical. Sand- 

 stone predominates and composes probably nearly 500 feet of the formation. It is usually 

 fine textured, but there are some coarse beds of no great thickness containing quartz pebbles 

 as large as marbles. Locally the sandstone is pitted with rounded iron stains the size of 

 buckshot, which seem to be due to the weathering of pyrite nodules. In places the sandstone is 

 cross-bedded. The intercalated limestone and shale are usually thin bedded and are generally 

 fossiliferous. The shaly member in the Finlay Mountains is about 100 feet thick. * * * 



The Cox formation * * * is conformably overlain by the Finlay formation, [which] 

 consists almost entirely of massive gray nonmagnesian hmestone, but locally thin beds of brown 

 sandstone are included. There are at least 300 feet of the Finlay formation exposed in this 

 region, but the top has not been found. * * * 



Rocks of Washita age are present as outlying masses in several localities. The thickness 

 of the strata is not great and it has not been found practicable definitely to correlate the 

 different exposures. They look much alilte, being commonly buff-colored calcareous shale and 

 thin-bedded limestone with occasional subordinate sandstone. 



H 14. LLANO-BURNET REGION, TEXAS. 



From his studies in 1910, the results of which are pubUshed in folio 183 of the 

 Geologic Atlas of the United States, Paige gives the following sections of the Llano- 

 Burnet region of Texas: 



In the Lland-Burnet region only the Fredericksburg and Trinity groups of the Lower 

 Cretaceous are represented. Although in the Austin quadrangle ° to the southeast, the Trinity 

 group was subdivided into the Glen Rose and Travis Peak formations, it was found impractical 

 for the following reason to make this distinction in the Burnet quadrangle. The Travis Peak 

 formation, while a definite lithologic and paleontologic unit in the southeast corner of the 

 Burnet quadrangle, loses these characteristics toward the north. This change is due to changes 

 in the conditions of sedimentation along a slowly subsiding coast line. Owing to the gradual 

 transgression of the sea over the land and the concomitant lowering of the surface which sup- 

 plied debris for sedimentation, the sediments grew finer and more calcareous, the basal beds 

 thinner and less conglomeratic, until a condition existed where only nearly pure limestones were 

 being deposited along low, gently sloping shores. The following formations have been mapped 

 in the Llano-Burnet area: The Edwards limestone; the Comanche Peak limestone, including the 

 Walnut clay; and the Trinity formation, including the undifferentiated Travis Peak and Glen 

 Rose. The following sections afford examples of the several formations. 



"Hill, R. T., and Vaughan, T. W., Austin folio (No. 76), Geol. Atlas U. S., U. S. Geol. Survey, 1902. 



