SUB-CARBONIFEROUS. 363 



thickness of Sub-Carboniferous between the Coal Measures and the Silurian in 

 the counties of Lampasas, San Saba, and McCulloch. He says:* 



" The older Paleozoic rocks of Llano and Mason counties were the chief land 

 areas from which the sediments composing the Carboniferous strata were de- 

 rived. Resting unconformably upon these rocks is a limestone, which is also 

 unconformable with the true Carboniferous. These beds appear as a narrow 

 strip, separating the Carboniferous from the Silurian, and consist almost en- 

 tirely of crystalline limestone with beds of shale. The beds of the Lower 

 Carboniferous series were formed mostly in rather deep water off the shore of 

 an old Silurian land area, and the beds of the sea shore may yet be seen in 

 the form of shales, and rarely conglomerates, in the bays and on the headlands 

 of the old shore line, which may be plainly traced. The dip of the beds is 

 somewhat variable, but the average is gentle, from one to two degrees north- 

 west. In one place the dip is twenty degrees in the same direction There 

 are small anticlinals and synclinals much more numerous than in the Upper 

 Carboniferous, where they are very rare. Unless carefully mapped and 

 studied over a considerable area, this formation might be overlooked ,and 

 classed as a portion of the Upper Carboniferous. The fossils resemble those 

 found in the true Carboniferous, though upon closer study some will un- 

 doubtedly be found to be quite different. One specimen of Goniatites has 

 been pronounced by Prof. Alpheus Hyatt to be a distinctive Lower Carbon- 

 iferous form. 



"The deceptive resemblance of fossils would at first lead to a decision that 

 these beds are a part of the Upper Carboniferous, and this deception is in- 

 creased when an actual contact occurs between the strata of the two forma- 

 tions. At two places east of San Saba the limestone seems to dip conforma- 

 bly beneath the sandstones. In both these places the dip of the strata of each 

 series is the same. It is only when we see the section as a whole that the 

 true relation of the two series is discovered. The San Saba River, from just 

 above its mouth nearly to the mouth of Richland Creek, is the dividing line 

 between the Upper and Lower Carboniferous, and this line of division is con- 

 tinued westward up the valley of Richland Creek. On the north side of this 

 line is the true Upper Carboniferous, consisting at this place of a great thick- 

 ness of sandstone. South of this line is the Lower Carboniferous, composed 

 in this region entirely of limestone and limy shales. As a person crosses the 

 region for the first time there are three possible explanations of such a rela- 

 tion of beds. The first is that the limestones and sandstones are interstratified ; 

 but this is quickly disproved, since in the sandstone areas there are no lime- 

 stones, and in the limestone regions no sandstones. This and abundant other 



* Preliminary Report on the Coal Fields of the Colorado River, Ralph S. Tarr. First 

 Annual Report of the Geological Survey of Texas, Austin, 1890, p. 201, et seq. 



