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argillaceous, porous limestone of the Tertiary Period. This rock reposes partly upon the sandstone last described, and partly upon Cretaceous strata, and contains imperfect fossils of the genera Tellina, Arca, and Infundibulum. The layers dip about two degrees east southeast.

Soil, during the latter portion of the day's march, a productive vegetable loam.

Distance, 20½ miles.

April 10.-Three miles from the last camp we came to another exposure of yellow argillaceous limestone of the Tertiary Period, containing fossils of the same character of those of yesterday. These strata constitute the prevailing surface formation for several miles, and nowhere exhibit a thickness of more than fifteen or twenty feet.

The rock yields readily to the action of the weather, and consequently would not be well adapted for building purposes.

The white pulverulent limestone, marls, and sandstones of the Cretaceous System underlay the limestone just described, the whole resting unconformably upon coarse sandstone, which sometimes exhibits a thickness of forty feet, and is usually coarse-grained and more highly ferruginous than that observed yesterday.

About one o'clock we arrived at Cibolo Creek, a fine stream of clear water, which at this point flows between high bluff banks, and has an average width of about forty feet. Here the sandstone is well exposed, exhibiting a thickness of near sixty feet above the bed of the creek. In this vicinity several large fragments of excellent iron ore were picked up. In fact strong indications of this metal were frequently observed during the day.

Shortly after crossing the stream we encountered heavy beds of millstone grit and coarse conglomerate. These strata continued to be largely developed during the remainder of our day's march, presenting frequent indications of local disturbance, and a general inclination of about fifteen degrees northwest. The conglomerate is of various degrees of hardness, and consists of metamorphic rocks, cemented sometimes with a silicious and sometimes with a ferruginous paste.

The surface of the country passed over during the day was more or less broken and hilly, and often covered to the depth of several feet with dark, rich, vegetable soil. Sub-soil calcareo-argillaceous, occasionally arenaceous.

Distance, 17 miles.

April 11.-Our road during the day was over a broken, hilly country. For the first few miles no change was observed in the character of the formation. The conglomerate was constantly exposed, occasionally exhibiting a thickness of forty feet. The sandstone and gritstone were also largely developed. In one instance a well was sunk to the depth of sixty feet, wholly through these beds.