Sandstone, though often covered at the surface by compact limestone or some other stratum is probably the rock which occurs in the greatest quantity throughout every part of this range of mountains. It is the prevailing stratum in all the country between the Arkansa and Red rivers, from the confluence of the Mamelle westward; rising to the height of two or three thousand feet, to form the summits of the Cavaniol, Sugar Loaf, and Mt. Cerne, and to a less considerable elevation at the Mamelle, Magasin, Caslete, and Short mountains. North of the Arkansa it forms the body of the Chattahoocke mountain, and of many nameless elevations, which diversify the surface from the sources of the Little Red river to the Mississippi. Beds of coarse conglomerate or puddingstone, are met with in many places; but these are particularly frequent in connection with the inclined or transition sandstones about the Washita. _Native Argil._--Nine miles west of Bainbridge, on {307} the road to Jackson, and on the right bank of the Mississippi, near the head of Tiawapeti bottom, also in various other places in this vicinity, there are extensive beds of perfectly white native argil, of about the hardness of common chalk, for which it has often been mistaken.[85] See Schoolcraft's "Catalogue of Western Minerals," art. 1st. Notwithstanding Mr. Schoolcraft's confident assertion, it must yet be considered doubtful whether any chalk has ever been found in the region under consideration. Specimens of the substance called chalk by the inhabitants, were collected at several places between Cape Girardeau and St. Louis. Also on the north side of the Missouri, on the road from St. Louis to Franklin. Some of these which were brought to New York, have been examined by my brother, Dr. J. James, and others, and were found to consist principally of argil, none of them occasioning the slightest effervescence with acids. This substance, whatever it is to be considered, is distributed extensively throughout the country lying around the confluence of the Missouri and Mississippi. Some specimens have been sent from Illinois to the Lyceum of Natural History at Troy, where they are spoken of as a "littrographic carbonate of lime;" but whether any experiments have been made to ascertain their real character we have not been able to learn. We have not, from our own observation, found occasion to confirm the statement, that nodules of flint are found imbedded in this substance; but we have commonly found it accompanied by the flint rock already mentioned, which has in many respects a manifest resemblance to the flints occurring in chalk formation. We have sought in vain for the remains of echini and other animals so common in chalk beds.