CARBONIFEROUS SYSTEM. 157 



thick is 140 feet above the bed of the river, while higher up the river, and 

 especially along the valley of the Concho, this same conglomerate is found in 

 the beds of the rivers in the lower valleys. 



It has no fossils in it, except the water-worn fossils of the surrounding for- 

 mations. It is usually bound together with calcareous material. The size of 

 the pebbles, and the fact that they are of the same material as the surround- 

 ing rocks, show that they have not been carried very far. These deposits are 

 from a few inches to 40 feet in thickness. They are sometimes two and three 

 miles wide. 



This conglomerate is found overlying all the formations when they form 

 the strata of the river valleys. I have never seen it on top of a high Creta- 

 ceous hill, either on the east or west of the eroded district; but it does occur 

 on top of the high Carboniferous hills on the eastern side of this great valley 

 of erosion. 



PETRIFIED WOOD. 



Petrified wood was seen at but two places, and at both of these localities it 

 was so situated as to lead me to believe that it did not belong to the strata in 

 the immediate vicinity, but had been carried there during the period of ero- 

 sion that destroyed the upper part of the strata in these places. 



The first locality where I found this material was on the south side of Cher- 

 okee Creek, five miles from its mouth. There was found only a single piece 

 about 3 feet long and 2 feet in diameter. It was on the side of a hill com- 

 posed of the massive limestones of the Carboniferous. There were other evi- 

 dences of drift in the large pebbles found there. 



The only other piece was found a few miles north of Brady. This was near a 

 bed of conglomerate composed of small siliceous pebbles, having an iron matrix, 

 and overlying the Carboniferous. At this place the fragments of what ap- 

 peared to have once been a single tree lay scattered over the surface of the hill 

 for a hundred feet or more. This piece must have been of gigantic propor- 

 tions, some of the pieces now being four or five feet long and two feet in di- 

 ameter. It will require closer examination of these woods than I was able to 

 give in the field to determine their character. These woods may assist in de- 

 termining the time at which the erosion was made and the conglomerate de- 

 posited. 



CAVES. 



Caves are very numerous in the limestones of the Carboniferous, and some 

 of them are very extensive. Very few of them have been explored for any 

 purpose other than idle curiosity. I entered only one of them, and traversed 

 it about three-fourths of a mile. Sometimes the roof would be high over- 



