244 
Transactions Texas Academy op Science. 
392. Taer, Ealph S. 
Origin of Some Topographic Features of Central Texas. 
• Amer. Jour, of Science, III, Vol. XXXIX, pp. 306-311. Xew 
Haven, April, 1890. 
“The Central Paleozoic area of Texas is a region of older rooks exposed 
hy 'the removal of the overlying uiiconformable Cretaceous. The southern 
portion of this area has, since the very earliest times, been the seat of 
extensive denudation as long as any land area remained above the sea. 
The Potsdam sandstone perhaps derived its sediment from the still older 
metamorphic rocks. :A conglomerate layer in the Lower Carboniferous 
series contains pebbles from the Silurian rocks. The same is true of the 
conglomerate in the Upper Canboniferous ; and the Trinity beds, the lowest 
of the Cretaceous system, when oonglomeritic, contain, in this region, 
chiefly Silurian (pebbles. The Quaternary drift has the same peculiarity.” 
The geological history of the region is now given with special reference 
to the Colorado river drainage. 
“The combination of geologic structure and peculiarity of erosion has 
given - rise to three types of topographic outline. First, the rugged hilly 
topography of the plicated and metamorphosed Silurian rocks, an outline 
in part descended from an existing Pre-Cretaceous topography. Second, 
a low hilly Oarboniferous area with many broad-topped hills, especially 
where the Cretaceous has just been removed. 'On account of the destructi- 
bility, this area is being rapidly degraded and the canon eharaoter of the 
Colorado is therefore rapidly disappearing, and thus destroying the evi- 
dence of the recent rejuvenation. Third, the sharp angular outline of the 
butte and meza type in the Cretaceous area which' is rendered possible 
by the nearly horizontal nature of the beds and the alternation of hard and 
soft strata, but which has proibably been aided also by the rapid erosion 
which followed the early Quaternary uplift.” 
393 ^ 
On the Lower Carboniferous' Limestone Series in Central Texas. 
Amer. Jour, of Science, Vol. XXXIX, p. 404. Xew Haven, 
May, 1890. 
“Mr. Tarr, in a recent communication to the editors, gives an account of 
his study of a Paleozoic region in Central Texas which was reported upon 
by Dr. F. Roemer in 1848 as affording fossils like those of the Carbonifer- 
ous limestones of the Mississippi Valley. The fossils described were from 
San 'Saba county. Mr. Tarr reports that the Paleozoic area covers part of 
iLlano, Mason, Southern San Saba and MoCulloch counties. The older 
rocks in it are much upturned and flexed; and the Silurian liniestones are 
chiefly manble, and have lost their fossils by metamorphism. Carbonifer- 
ous limestones and shales overlie these beds unconformably, and the Upper 
Carboniferous consisting of sandstones, shales, clays and limestone, ‘attain 
a thickness in one section of 8^000 feet.’ ” 
