Proceeding westwardly across the meridian above specified, the hilly country gradually subsides, giving place to a region of vast extent, spreading towards the north and south, and presenting an undulating surface, with nothing to limit the view or variegate the prospect, but here and there a hill, knob, or insulated tract of table-land. At length the Rocky Mountains break upon the view, towering abruptly from the plains, and mingling their snow-capped summits with the clouds. On approaching the mountains, no other change is observable in the general aspect of the country, except that the isolated knobs and table-lands above alluded to become more frequent and more distinctly marked, the bluffs by which the valleys of watercourses are bounded present a greater abundance of rocks, stones lie in greater profusion upon the surface, and the soil becomes more sandy and sterile. If, to the characteristics above intimated, we add that of an almost complete destitution of woodland (for not more than one thousandth part of the section can be said to possess a timber-growth) we shall have a pretty correct idea of the general aspect of the whole country. The insulated tracts herein alluded to as table-lands, are scattered throughout the section, and give to the country a very remarkable appearance. They rise from six to eight hundred feet above the common {224} level, and are surrounded in many instances by rugged slopes and perpendicular precipices, rendering their summits almost inaccessible. Many of them are in this manner completely insulated, while others are connected with the plains below by gentle acclivities, leading from their basis to their summits, upon one side or other of each eminence. These tracts, as before intimated, are more numerous, but less extensive in the vicinity of the Rocky Mountains than they are farther eastward; and in the former situations, they are more strikingly characterized by the marks above specified than in the latter. The geological formations that present themselves along the declivities of those heights are principally horizontal strata of secondary sandstones, and breccia or puddingstone, alternating with each other. Clinkstone prevails upon the surface of them in many places, but in general the superior strata are rocks of the description just before mentioned. These tracts are denominated tabular, not from any flatness of surface by which they are characterized, but from their appearance at a distant view, and from the horizontal disposition of the stratifications imbedded in them. Their surfaces are usually waving, and in some instances rise into knobs and ridges of several hundred feet high; many of them are clad in a scanty growth of pitch pine, red cedar, scrubby oaks, &c., while others exhibit a bald or prairie surface.