I have employed a short period of leisure in passing over a portion of the state of Indiana. Among other objects, I was not wholly inattentive to the mineralogical and geological features of the country. I now, with diffidence, transmit to you the result of my inquiries. SKETCH, &c. The secondary formation of the state of Indiana is abundantly evident. The surface of the soil is undulating, and marked with few elevations which deserve the name of mountains. The rocks are sandstone, limestone, and clay-slate; all of which are disposed in horizontal strata. The sandstone presents nothing remarkable in its appearance. Its colours are various shades of gray and brown. The principal hills are of this formation. The principal colours of the limestone are blue and gray, and their various mingled and intermediate shades. Its secondary formation is very manifest from its almost earthy appearance. In innumerable instances, the limestone rocks contain immense quantities of imbedded shells, of great similarity in form and appearance, and having considerable resemblance, to the common escallop-shell of the ocean. Owing to the easy decomposition of these rocks, and the horizontal position of their strata, they afford many subterranean passages for water. A considerable stream, called Lost River, runs into a cave in the side of a precipitous hill; and, after a passage of 6 or 7 miles under the earth, again makes its appearance, with a large accession to its waters. The traveller's attention is continually excited by cavities in the earth, where the temporary rivulets, proceeding from rains, make a sudden exit through perpendicular perforations in the upper stratum of the rock. There are many such cavities, which do not receive any water from the surface. Some of them are many yards in diameter, forming a regular circular concave, of considerable depth towards the centre. They are vulgarly known among the inhabitants by the name of "_sink-holes_." The localities of slate are few, and present nothing uncommon.