THE C EN O ZOIC DEPOSITS OF TEXAS. 557 



slight blow of the hammer. Local beds of conglomerate occur, 

 and, on the Nueces, a heavy bed of black flint gravel was traced 

 from its outcrop until the dip carried it below the water line. 



As I now understand this division, the base is found at La 

 Grange bluff, described by Penrose, 1 and it embraces the beds 

 from which the fossils came which were reported by Shumard 

 (Trans. St. Louis Academy, 1863, p. 140) and determined by 

 Leidy (Proc. Phil. Ac. Nat. Sc, 1865, p. 176, and 1868, p. 231, 

 etc.). 



Mill creek, between Brenham and Burton, marks a lithol- 

 oafical change, the rocks west of that stream, which are the 

 lower, being more compact than those east, which at Brenham 

 have the character of cross-bedded grits with pebbles of clay, 

 containincr water-worn cretaceous fossils, as well as numerous 

 fragments of the bones of vertebrates. A similar division was 

 noticed east of La Grange. 



On the Nueces the beds, which are here highly saliferous, are 

 well exposed from Oakville to Fort Merril, at which place they 

 are overlaid by the Pliocene. Here begin the silicifications of 

 portions of the materials, which becomes a more and more 

 prominent feature of the deposits further west. 



Among these silicifications may be mentioned the rocks, 

 known as Las Tiendas, on the road between San Diego and 

 Tilden. On the outside these rocks resemble masses of light- 

 colored flint, the surface of which is highly polished by blown 

 sands. Closer examination shows that they are simply portions 

 of the interbedded clays and sands of the Oakville beds, which 

 have become silicified without destroying the original structure 

 of the beds. Thus the bedding and lamination is apparent in 

 portions of the mass, and the siliceous pebbles, so common in 

 the unaltered beds, are found in these masses also. 



To the same a^e as the Oakville beds I have also referred 

 the range of hills in the valley of the Nueces, known as the 

 Picachos. 



These hills, running northwest and southeast, are nowhere 



1 First Annual Report, Geological Survey of Texas, p. 54. 



