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on both sides of the gap a distinctly red appearance, thus giving additional evidence to the extremely local derivation of the varying Trinity beds.

From Big Spring westward for one hundred miles the geological structure is undoubtedly Cretaceous though in a few small isolated patches the Permian may come to the surface. The first indication of the undoubted Cretaceous is in a railway cut two miles east of Big Spring. A small syncline here exposed in section has a southeast axis and a dip in one place as great as ten degrees southwest and five degrees northeast.

The width of the syncline is not more than 100 feet in the exposed section.

Beginning at the base the section is:

Conglomerate grading into the lower sandstone, and composed of pebbles generally as large as a nutmeg and larger. Pebbles are quartzite and other metamorphic rocks (hornblendic, etc.,) and considerable limestone, resembling that of the Coleman division. The small pebbles are generally well rounded, but the larger ones are often quite angular. The cement is limy and in places magnesic.

This conglomerate resembles quite closely the Trinity conglomerate of the Cretaceous, and it may belong to this age. Several specimens of oysters were found in the conglomerate, but they are in such a poor state of preservation that it is quite impossible to determine them.

On the railway, 2½ miles west of Big Spring, there is a cut in an impure clayey greensand, from which bones were collected. No other fossils were found in this vicinity. Above this sand is a yellow sand overlaid by an unfossilliferous magnesic limestone. Chiefly from the character of the overlying beds I conclude that this stratum is a member of the Trinity division of the Cretaceous, and this conclusion is rendered the more-probable from the occurrence of the oyster-bearing bed beneath it east of Big Spring.

CRETACEOUS NEAR MARIENFELD.

The strata in the bluffs bordering the valley of Girard creek have a general reddish hue toned down in intensity by lighter colored sands. These may be Trinity beds with a red color derived from the underlying Permian, though of this I can offer no definite proof.

From this point westward the country is a gently undulating plain without any abrupt rises or marked hills, but with a general ascent westward. There is little to indicate the geological structure in this section, but the soil is sandy, and it is probable that the strata exposed in Girard creek continue for this distance. Three miles east of Marienfeld a peculiar mottled limestone appears above the sand. It has a