146 APPENDIX D. GEOLOGY. 



The branches of Red river have cut deep chasms in this formation. 

 In some places they are spoken of as fifty, and in others as two hundred 

 feet deep. This clay, worn away by the streams, and mechanically sus- 

 pended, gives that red color to the water, from which, without doubt, 

 was derived the name of Red river. As to the substances held in solu- 

 tion by the waters of that river, some further description will be desirable 

 before mentioning them. 



The red chy formation above described abuts against the Witchita 

 mountains, occupying the lower and more level regions around their 

 base. Here we have an outburst of unstratified rocks, which are satis- 

 factorily represented in the specimens. 



If the relative position of the red clay and sandstone on section XI is 

 correctly shown, I should infer some disturbance in the stratified de- 

 posites, which would indicate a more recent upheaval of the mountains 

 than might be inferred from the nature of the rocks. The principal one 

 is a red granite, with a great predominance of feldspar, and the almost 

 total absence of mica. Porphyry also occurs in great quantity, of a 

 reddish color, the imbedded crystals, for the most part, being red feld- 

 spar. In the easterly part of these mountains this rock is developed on 

 a large scale, forming smooth, rounded hills, which slope gradually down 

 to the plain. Cache creek passes through one of these hills, forming a 

 gorge from three hundred to four hundred feet high, with " smooth, 

 perpendicular walls." This rock Dr. Shumard calls prophyritic green- 

 stone, and one of these walls is shown on section XI. He says that the 

 rock is slightly columnar. 



The rocks of these mountains are traversed by veins of greenstone 

 and quartz. The latter is often porous and colored by the oxide of 

 iron. The greenstone is the most recent of the unstratified rocks among 

 my specimens, save a single vesicular mass, broken probably from a 

 boulder, wdiich has all the external marks of lava. It looks more like 

 recent lava than any specimens I have ever met among greenstone or 

 basalt. It was collected June 15th, west of the great gypsum deposite, 

 though in a region abounding with sandstone, and near the bluffs that 

 form the border of the "Llano estacado." Dr. Shumard found in the bed 

 of the Red river, near the same place, what he calls greenstone, green- 

 stone porphyry, and trachite. The specimen to which I have referred is 

 rather augitic than trachitic. He says, also, that he found there " black 

 scoria, and several other specimens of volcanic rocks." Again, on ap- 

 proaching the Witchita mountains on the return trip, he describes one 

 as "a truncated cone, with a basin-shaped depression in the summit." 

 Of this he seems to have judged by looking at the mountain from a 



