78 INDEX TO THE STKATIGEAPHY OF NORTH AMERICA. 



Feet. 

 Covered; mostly sandy shales. At bottom a 2J-foot bed of red conglomerate sandstone with, flat 



pebbles; a few shell fragments in this ledge 10 



Mostly fine-grained dirty- white, brown, yellow, and red sandstone 45 



Massive pink and white, conglomerate sandstone, with white quartz pebbles mostly one-half 

 inch in diameter; cross-bedded; prevailingly reddish tones. Near top grains are smaller and 

 more rounded. Secondary infiltration of quartz in cross fractures gives honeycomb structure 

 on weathering 85 



567 



It will be noted that the sections are not complete. The following measurements include 

 the upper portion of the Cambrian, or the Wilberns formation: 



Generalized section of Wilberns formation on east bank of Colorado River about one-third mile 



above old Tanyard Crossing. 



Ellenburger limestone at top. Beet. 



Impure limestone ■. 30 



Heavy-bedded limestone containing abundant exceedingly small shell fragments, also abundant 



minute globular remains 10 



Impure sandy limestone having conglomerate aspect in the hard layers 10 



D6bris-covered slope 10 



Debris-covered slope; contains layers of shale conglomerate consisting of cemented flat fragments 



of thin shale accompanied by layers containing bowlder-like forms composed of limy mud 60 



Slope of impure limestone layers breaking down to 1 inch in thickness, carrying fine sand, 



weathering light brown 30 



Pink flaggy semicrystalline limestone 10 



Crystalline and semicrystalline bedded limestone, weathering into hard layers 11 



Heavy layer of mottled light-brown impure limestone 4 



Alternating beds of crystalline limestone, 4 inches to 1 foot thick, with crinkly-weathering beds 

 that are slightly more sandy, the whole carrying finely disseminated glauconite, locally concen- 

 trated in layers 23 



Base, recent silt of Colorado River. 



Another section of the Wilberns is as follows: 



Generalized section of Wilberns formation near head of Little Llano River. 



Ellenburger limestone at top. Feet. 

 Calcareous shale, with subcrystalline to crystalline oolitic limestone bands; alternating hard and 



soft 39 



Thin flaggy limestone with some sandy layers 10 



Shale and shaly limestone and subcrystalline layer with shell fragments 11 



Conglomerate containing slightly rounded half-inch to 1-inch pebbles, weathering yellow, wilih 



limestone matrix , 1 



Greenish-gray shales 6 



Two beds of conglomerate, about 8 inches each, separated by 8 inches of shale; small, slightly 



rounded calcareous pebbles weathering yellow 2 



Fine-grained greenish-gray shaly limestone 3 



Conglomerate of long, flat, thin, shaly calcareous fragments, overlain by fine-grained calcareous 



muds 3 



Greenish shaly limestone 5 



Conglomerate composed of small, slightly rounded calcareous pebbles weathering yellow IJ 



Light-gray shaly limestone, weathering to a covered slope 25 



Thicker-bedded gray crystalline limestone, with scattered grains of glauconite; a few hard layers 



about 9 inches thick 20 



Light-pink to gray thin-bedded flaggy crystalline limestone, mottled brown by fine-grained sand . . 17 



Pink and gray crystalline limestone ; glauconite grains at base 6 



Pinkish subcrystalline limestone 7 



Sandy limestone and a little glauconite 2 



Base at top of glauconite sand. ' ^ 



