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many small pebbles, generally less than the size of a pea, though with a few as large as a nutmeg. The cement is in places magnesic.

The Iatan mesa appears to dip as much as two degrees S. E., and a southeast dip has been quite noticeable since leaving the Colorado.

Between Iatan and Big Spring the surface of the country undulates considerably with a general rise to the west to within six or seven miles of Big Spring, when the valley of Girard creek, a large branch of the Colorado, is reached. The soil is chiefly sandy with some red clay. Near Girard creek the soil is very sandy, the sand being derived from a calcareous or magnesic white sandstone, which outcrops for some distance east of Big Spring. To the south and west are a series of buttes and mesas, the most remarkable of these being Signal mountain on the west side of Girard creek. This butte, apparently perfect in outline from any view, stands out as an outlier entirely isolated from the mesa. From the base of the mesa, south of Big Spring, a great body of constantly flowing water comes to the surface, forming the water supply of that town.

While the conglomerate east of Girard creek is plainly post Permian and probably lower Trinity, and the beds described west of the creek are probably of corresponding age, it is quite possible that the white sands of Girard creek are still Permian.

The type of erosion west of Big Spring is interesting. Girard creek, so called, is not a creek in any sense of the word. There is a broad valley, but without extraordinary floods water cannot flow in it. For six miles the railway follows up this valley, then the valley turns northward into the Llano Estacado. The average width of the valley is not more than a mile, and the borders are more or less degraded bluffs, sometimes quite abrupt, and generally from 50 to 100 feet in height. There is no channel, but here and there a lagoon, generally no more than a bog or an alkaline flat without vegetation of any kind. The valley has apparently been deeper, and it is now filled with sediment probably in part brought down from time to time whenever excessive rains furnish water enough to permit of its flowing, as I am informed is sometimes the case. Much of the detritus with which the valley is at present clogged is derived from the neighboring cliffs in time of rain, and is deposited in the form of local and temporary deltas. The general appearance of the valley is that of a shallow estuary in the marshy country of the seacoast of the northeastern states. This resemblance is increased by the presence of barren flats without vegetation and the presence in places of a coarse salt grass, whose habitat is a damp clayey alkaline soil. Much of the valley is occupied by low mounds (cone deltas) and mesquite flats, and one would not suspect that water ever flowed in the valley.