364 GEOLOGY OF NORTHWESTERN TEXAS. 



field evidence proves that the limestone is beneath the sandstone; and then 

 the problem is narrowed down to two possible solutions — the two series are 

 either conformable or unconformable. There are two proofs that they are 

 not conformable. The dip of the limestone averages at least two hundred 

 feet to the mile, and with such a dip any bed of limestone, as for instance the 

 bed on the Colorado below Red Bluff, would soon dip under the sandstone if 

 followed a few miles to the west, and the overlying sandstone would cover it 

 and extend to the Silurian. But such is not the case. The belt of limestone 

 extends continuously for nearly thirty miles. In this series there are many 

 different beds of limestone and shale, one above the other, each one of which 

 strikes up to the sandstone and there stops. 



"We have therefore an upper sandstone formation, composed of various 

 beds, striking southwest and overlapping a great thickness of limestone. There 

 is therefore no explanation, to my mind, but unconformabihty; a fact which 

 necessarily proves a different age from that of the overlying coal measures. 

 That they are Lower Carboniferous rather than Devonian is shown by the 

 close resemblance of the fossils of the lower beds to those of the Upper Car- 

 boniferous. The field evidences thus seem to prove that these beds are not a 

 part of the true coal bearing series, but belong to an older formation — the 

 Lower Carboniferous. The Lower Carboniferous extends from near Lam- 

 pasas to some distance west of Brady, with an average width of not more than 

 ten miles, and is the formation on which the towns of San Saba and Brady 

 are situated." 



His reference of these deposits of shales, limestones, and rarely conglomer- 

 ates, to the Sub-Carboniferous, is based upon: 



1. Unconformability with underlying Coal Measures strata. 



2. Paleontology. 



My investigations, made both before and after those recorded by Mr. Tarr, 

 do not seem to me to warrant the reference of these beds to any period 

 earlier than the Coal Measures themselves. 



That there is non-conformity between the limestone and the sandstone beds 

 in places there is not the slightest doubt, and the non-conformity is probably 

 even greater than Mr. Tarr states it to be. He only claims difference of de- 

 gree of dip, while in fact there is also difference in direction. 



I think that it will be readily apparent that given the old Silurian shore 

 line which Mr. Tarr describes, with its headlands and bays, having a general 

 trend east and west, the dip and strike of the strata at its foot would naturally 

 be governed more or less by the contours of its eroded surface and the shore. 

 That this is the case is evidenced by the carefully prepared maps of the area 

 made by Mr. Tarr, now in the possession of the Survey. These show in sev- 

 eral places the strata in question dipping away — northeast, north, northwest — 



