As the scientific division of the Expedition was fully organized previous to our leaving Indianola, it was thought advisable to commence the geological investigations at that point.

The country in the vicinity of Indianola is for the most part flat, and but little elevated above the adjacent bay of Matagorda. It is traversed in different directions by long, narrow lagoons, whose depths vary from a few inches to fifty feet. These are apparently diminishing in size, while the dry beds of others, often containing thick accumulations of Ostrea and other marine shells of existing species, and the low, flat character of the surface generally, proclaim this region to have been but recently recovered from the domain of the Ocean.

The Geological Formation here consists of alluvial deposits of tough calcareous clay, of light blue and red colors, and fine yellow calcareo-silicious sand. The sand is a more recent deposit than the clay, and is arranged chiefly along the coast in nearly parallel ridges, from five to twenty feet in height, thus constituting a kind of natural levee. As these ridges coincide with the various indentations of the coast, and are largely composed of finely comminuted shells, they are doubtless the result of the conjoint action of the waves and wind; the former throwing the materials up, the latter transporting them inland.

We left Indianola on the 4th of April, the general direction to be pursued from this point to San Antonio de Bexar being nearly northwest.

During the first day's march we traveled over gently undulating prairie, composed of alluvial deposits of tenacious clay and dark silicious sand; the