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and may generally be easily recognized, even at a distance, by the deeper color of the grass growing upon them. These soils are also remarkably well adapted as fertilizers, for which purpose they will doubtless hereafter be extensively employed.

Calcareous Soils.-The soils overlying the limestone of the Upper Cretaceous group usually contain a very large proportion of carbonate of lime, which, indeed, is sometimes present to such a degree as to render the land entirely unproductive. When mixed, however, as is usually the case, with a fair proportion of other ingredients, a highly productive marl is formed.

Soils of the Paleozoic Period.- Although generally less favorably constituted than any of the preceding, many of the soils derived from the decomposition of the Paleozoic rocks are, owing to the more favorable meteorological conditions of the regions in which they occur, far more productive. These do not present a great deal of difference in general mineralogical composition, but vary considerably in the amount of vegetable matter they contain. They consist chiefly of lime and silica in different proportions, with an admixture of alumina, iron, and vegetable matter.

Soils of Igneous Rocks.-Few of the soils derived directly from the igneous rocks have been found of much value. They are generally loose, of a deep red or brown color, and are composed mainly of quartz and felspar in coarse and fine particles. - When they contain small quantities of clay, lime, or gypsum, as is sometimes the case along the streams, they become highly productive and are clothed with rich vegetation.

Water-worn pebbles are of frequent occurrence in the beds of the different streams of Texas and New Mexico. They are derived mainly from the Boulder Formation and older rocks, and exhibit almost every variety of composition. In the beds of the Upper Brazos, Big Witchita, and Red Rivers, they are sometimes accumulated to the depth of four or five feet.

Various metallic ores, as copper, iron, and manganese, have been found in connection with these deposits. In Otter Creek, a small affluent of Red River, having its source in the Witchita Mountains, two small specimens of bluish-yellow quartz, containing gold in small quantities, were found.

To the Alluvial Period we must refer those accumulations of loose sand which occur in the beds of nearly all the streams of Texas, New Mexico, and the adjacent Indian Territories, and which are also occasionally met with in situations remote from existing water-courses. The latter sometimes cover many square miles of surface, and appear to be continually shifting their position. Examples of these shifting sands are to be met with near