302 CENTRAL MINERAL REGION OF TEXAS. 



anywhere observed, but there is good warrant for dividing the series into two 

 divisions. These are here named: A, The Hinton Division, and B, The Deep 

 Creek Division. 



A. THE HINTON DIVISION (BIRDSEYE, BLACK RIVER, AND TRENTON?) 



The distribution of the lower division, if such it really be, is apparently very 

 much restricted within the limits of our district, and yet is represented by 

 thick deposits of unusual interest. The region of greatest deposition seems 

 to have been in the northwest, and the present positions of the beds give 

 vague hints of gradual movements of elevation and depression along lines 

 which have not been clearly defined. 



The following generalized section is made up from different exposures 

 south of the San Saba River in San Saba County, in the valleys of Deer and 

 Hinton creeks, one of the best regions for study. This agrees well, also, with 

 the partial outcrop on Cold Creek, in Llano County, and with an incomplete 

 development of the series on Hudson Creek, north of Camp San Saba, and 

 westward in McCulloch County. Beginning below there are: 



1. A transition set of siliceous limestones of variable thickness, and some- 

 what indefinite composition, making it difficult in some sections to draw a 

 sharp line. Occasionally a semi-conglomerate of limestone fragments occurs 

 here, as on Cold Creek, at Sponge Mountain. 



2. A pink, white, or mottled red and white limestone, with crystalline 

 facets, agreeing well with the typical Birdseye Limestone of New York and 

 elsewhere. Thickness usually not above 15 feet. 



3. Tough, commonly dull gray to brownish, crystalline dolomites, weath- 

 ering gray, usually in some variety. In this set, two miles west of San Saba, 

 on the road to Brady, I took from a block of limestone Maclurea crenulata, 

 Billings, and Favosites, sp.? 



4. Sometimes a set of calcareous shaly beds, 15 to 20 feet. 



5. A fossiliferous horizon with a solid pavement of large sponges — Stro- 

 matocerium rugosum, Hall, or a near ally. In some cases there are beds of 

 these fossils at least 1 feet thick. 



6. An aggregation of sandy calcareous shales or slabby dolomites, usually 

 forming cliffs or craggy outcrops; 25 to 30 feet. 



7. A sponge bed made up of strata of slabby character, containing exces- 

 sive quantities of what seems to be Stromatopora concentrica, Hall; from 15 to 

 20 feet. 



Here the section stops in many instances, and a hiatus in our knowledge 

 occurs which has not been completely filled, owing to great faults and through 

 lack of notes upon any one exposure, including these beds with both higher 

 and lower beds. But there is reason for assuming the base of the higher 

 division to be just above the summit (No. 7) of this section. In the plateau 



