Discussions of this sort have been much insisted on of late, and may be important as aiding in the geography of climates and soils, but can afford little assistance to topography. {319} The geognostic features of the region under consideration, afford some foundation for a natural division, but this division must be so extremely general as to afford little satisfaction. We could only distinguish the red sandstone, the argillaceous sandstone, and the trap districts, and though each of these have distinctive characters not easy to be mistaken, they are so irregular in form and position, as to be in no degree adapted to aid in the description and identifying of particular places. On the contrary, it is to be regretted there are no established points to which we might refer, in communicating what we have observed of the position of these formations, and indicating the particular localities of some of the valuable minerals they contain. The red sandstone, apparently the most extensive of the rocky formations of this region, has, wherever it occurs, indications of the presence of muriate of soda, and almost as commonly discloses veins and beds of sulphate of lime. The substance last mentioned had been growing more and more abundant since we left the region of the trap rocks at the sources of the river. It was now so frequent as to be conspicuous in all the exposed portions of the sand-rock, and was often seen from a distance of several miles. It occurs under various forms, sometimes we meet with the most beautiful selenite, disposed in broad reticulating veins, traversing the sandstone; the granular and fibrous varieties, whose snowy whiteness contrasts strongly with the deep red and brown of the sandstone, are sometimes seen in thin horizontal lamina, or scattered about the surface, sometimes included in larger masses of the common amorphous plaister-stone. This last is usually of a colour approaching to white, but the exposed surfaces are more or less tinged with the colouring matter of the sand-rock, and all the varieties are so soft as to disintegrate rapidly when exposed to the air. Recent surfaces show no ferruginous tinge; {320} or rather, we would say, this colour does not appear to have been contemporaneous to the formation of the sulphate of lime, but derived from the cement of the sandstone, and to have penetrated no farther than it has been carried by the impetration of water.