PALEOZOIC ROCKS. 661 



sent to Dr. H. S. Williams, of Ithaca, New York, for identification. Await- 

 ing his report, which can not appear herewith, I retain the term Devonian 

 provisionally, and merely add that the superficial extent of the terrane has 

 been materially extended since the 1889 Report. The rocks included lie as 

 an inner fringe about the edge of the known Carboniferous, being well de- 

 veloped on Wallace Creek and westward, and on the lower part of Cherokee 

 Creek, in San Saba County, somewhat also in Lampasas County, and more 

 than anywhere else in the hills south and southwest of Marble Falls, between 

 the Colorado River and Slick Rock Creek, on the road from Marble Falls to 

 Llano. The same terrane outcrops below Marble Falls near Double Horn, 

 also at Marble Falls and back of it on the hills, as well as in the river bed 

 itself, being in juxtaposition, along fault lines, with Silurian and Carbonifer- 

 ous strata. 



THE CARBONIFEROUS SYSTEM. 



The Carboniferous rocks have been studied by other members of the Sur- 

 vey where they touch this district upon the north. 1 have examined only 

 such exposures as could not be observed by them. These consist of isolated 

 patches, chiefly upon the south. 



If the Devonian be a reality, as assumed in this Report, there is as yet an 

 uncertainty regarding the horizon which must be taken for its summit An 

 interesting series of black shales overlying the fossiliferous beds has usually 

 been considered Carboniferous, but mainly from its supposed parallelism with 

 a higher set of fossiliferous shales outcropping along the northern border. 

 We have not yet the data for correlating the separated exposures, but it is 

 very possible that the Hamilton Creek shales here referred to should rightly 

 be included in the Devonian. They are. however, closely related in age to 

 the beds which contain a thin (two inches to six inches) seam of coal in this 

 region, and it will be best still to relegate them to the Carboniferous. The 

 exposures are mainly in the lower valley of Hamilton Creek and along the 

 Colorado River below this, running up a short distance into Panther and Coal 

 creeks, and the creeks coming in from the opposite bank of the Colorado, all 

 in Burnet County. Some of the same rocks occur in an isolated patch south- 

 east of Cypress Mill, in the Pedernales Canyon, in Blanco County; a limited 

 and insulated outcrop is peculiarly exposed in Honey Creek Cove, in the Ri- 

 ley Mountains, Llano County, and there is also a patch, chiefly of higher Car- 

 boniferous beds, in the Llano River valley below the old Beef Trail Crossing, 

 above the mouth of Big Saline Creek, in Kimble County. Included in many 

 of these areas are strata of undoubted Carboniferous age. I have also had 

 occasion to examine certain exposures in the San Saba River valley, at the 

 mouth of Five Mile Creek, in Mason County, and others upon Wallace and 

 50— geol. 



