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 formations. 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 surrounding 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 Cretaceous 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 erosion 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 Cherokee 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 composed of the massive limestones of the Carboniferous. There were other evidences 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 appeared 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 proportions, some of the pieces now being four or five feet long and two feet in diameter. 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 determining the time at which the erosion was made and the conglomerate deposited.

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 overhead,