368 The American Geologist. June, i89i 
and intervening Tertiary basins of the Texas-Mexican region. 
From San Antonio westward to Del Rio, and thence southeastward 
through Mexico to an indefinite distance coastward beyond Lam- 
pazos, Mexico, included between the eastward escarpment of the 
Comanche series plateau of Comal, Uvalde, Medina and Maverich 
counties and the Santa Kosa mountain group of Mexico, at an 
elevation of 400 to 1000 feet above the Rio Grande, there are pre- 
served man} r remnants of a grand detrital deposit of either a fresh 
water lake or a great embayment of the gulf which existed in 
comparatively recent Tertiary or Quarternary time. This deposit is 
composed of flint and limestone pebbles and boulders of material, 
mostly from the Comanche rocks, cemented by a calcareous ma- 
trix. Terraces, benches and remnental patches of this material 
are found around the perimeter of the whole area in great thickness, 
while estuarine embayments extend far up the canons of the 
streams flowing into it from the mountain. The caiion Rio Frio 
in Uvalde county, Texas, for instance, gives a fine view of this 
fact. While the headwater erosion of that stream is still progress- 
ing, and destroying the grand Cretaceous plateau of Edwards and 
Uvalde counties, the lower half of the caiion, from one to three 
miles in width, is a level valley filled with fifty feet of this ancient 
debris, through which the stream is now cutting. I propose the 
name Uvalde formation for this terrace and shall discuss it more 
fully in future papers. 
The Age of the Strata at Marble falls and Shinbone ridge. 
In the American Geologist for November 188Q, I published a 
paper entitled ' ' A Portion of the Geologic Story of the Colorado 
River of Texas," in which I assert the rocks of Marble Falls and 
the adjacent Shinbone ridge in Burnet county, Texas, to be of 
Carboniferous age. Inasmuch as my determination of the fossils 
were made by professor H. S. Williams of Cornell' University, 
who is our best American authority on the later paleozoic rocks, 
I was somewhat surprised to read in Dr. Theodore B. Comstock's 
paper on the "Geology of the Central Mineral District" in the 
First (Second) Annual Report of the Texas State Geological Sur- 
vey, that he had proved "beyond all doubt" that my conclusions 
were wrong, and that the strata at Marble falls were "Devonian" 
and those of Shinbone ridge "Silurian. " Inasmuch as he gave no 
paleontologic or other reasons for this remarkable diversity in age 
of the same stratum, I recently revisited the region in company 
