POST-PALEOZOIC UPLIFTS. 313 



here referred to a later age, and the question of the relative age of this and 

 the associated rocks is not now involved. The details of this Post-Carbon- 

 iferous dynamic history must largely be worked out by one familiar with 

 what we have been studying here. It is therefore appropriate for us to in- 

 quire into the nature of the problems which still remain to be worked out; 

 for it has been manifestly impossible to give attention to more than the salient 

 features in the time heretofore at our disposal. One of the best fields for the 

 investigation is the extremely rugged area of the Riley Mountains, whose 

 relief has been erroneously recorded upon all previous maps. A little expe- 

 rience in that region has well shown the absolute necessity for doing good 

 topographic work there as a basis for geologic study. 



In the northern end of that ridge, at the source of Honey Creek, the Silurian 

 upon a high plateau, abuts against an outer rim of Cambrian rocks along an 

 east-west fault. The strike of the Hoover beds is there in line with the Post- 

 Silurian uplift, but farther south and east, upon the south side of Honey 

 Creek Cove, the faults and strikes are mainly parallel with the Post- Paleozoic 

 disturbance, and the latitudinal trend is beautifully shown by the highly tilted 

 strata, not dipping in one direction, as Mr. Walcott has remarked, "from 

 10 degrees at the north end of the ridge to 40 degrees at the south end," 

 but varying in strike through faults which give such an appearance upon 

 cursory examination. This upheaval is more or less evident over all the 

 country in line with it, wherever the rocks are adapted to show it; but its 

 modes of expression are various. It will be many years before the details 

 of some of the structure are worked out. A few points of interest have 

 been noted, and these are all we can now present. , 



From the mouth of Hamilton Creek, Burnet County, and perhaps farther east 

 up the Colorado River to the mouth of Big Sandy Creek, and up that stream 

 to its source, thence on across country in the same course, as far as the Cre- 

 taceous escarpment upon the west in Kimble County, the continuation of 

 this orographic movement may be readily traced. In this distance of eighty 

 miles, and over a tract of thirty-five miles on either side of this line, the only 

 known exposure of Carboniferous rocks is this limited one in the Riley Moun- 

 tains, which has been faulted, downthrown, tilted, and denuded, and it exhibits 

 none of the earlier trends. 



About three miles east from this exposure stands Packsaddle Mountain, 

 scored, fissured, and eroded, about as diverse in its structure and as different 

 from the Riley Mountain types as could well be, and yet epitomizing, in 

 effect, the same dynamic events, with those of earlier date as well. 



In Mason County, on the divide between Honey and Little Bluff creeks, 

 south of the Mason and Junction City road, Fernandan, Texan, Cambrian 

 and Silurian strata are jumbled by three or four of the dynamic movements, 



