James's Account of S. H. Long's Expedition, 1819-1820, part 4

by Edwin James; Stephen H. Long; Thomas Say

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.

By far the greater proportion of this section of country is characterized by a rolling and plain surface, which may be alleged not only of the space included within the limits above assigned, but of extensive portions of country north and south of it. Although the elevated table-lands, a description of which has just been given, are situated within this region, they occupy but a small proportion of it. In addition to these inequalities in the surface of the country, there are numerous mounds or knobs of different magnitude, and occasionally swells of greater {225} or less extent, which contribute to give a pleasing variety to the prospect. The country is also divided into extensive parterres by the valleys of rivers and creeks, which are usually sunk 150 or 200 feet below the common level, and bounded in some places by perpendicular precipices, and in others by bluffs, or banks of gentle slopes.

Immediately at the base of the mountains, and also at those of some of the insular table-lands, are situated many remarkable ridges, rising in the form of parapets, to the height of between fifty and one hundred and fifty feet. These appear to have been attached to the neighbouring heights, of which they once constituted a part, but have, at some remote period, been cleft asunder from them by some extraordinary convulsion of nature, which has prostrated them in their present condition.

The rocky stratifications, of which these ridges are principally composed, and which are exactly similar to those of the insulated table-lands, are variously inclined, having various dips, from forty-five to eighty degrees.

Throughout this section of country the surface is occasionally characterized by water-worn pebbles, and gravel of granite, gneiss, and quartz, but the predominant characteristic is sand, which in many instances prevails almost to the entire exclusion of vegetable mould. Large tracts are often to be met with, exhibiting scarcely a trace of vegetation. The whole region, as before hinted, is almost entirely destitute of a timber-growth of any description. In some few instances, however, sandy knobs and ridges make their appearance, thickly covered with red cedars of a dwarfish growth. There are also some few tracts clad in a growth of pitch pine and scrubby oaks; but, in general, nothing of vegetation appears upon the uplands but withered grass of a stinted growth, no more than two or three inches high, prickly pears profusely covering extensive {226} tracts, and weeds of a few varieties, which, like the prickly pear, seem to thrive best in the most arid and sterile soil.

In the vicinity of the Rocky Mountains, southwardly of the Arkansa river, the surface of the country, in many places, is profusely covered with loose fragments of volcanic rocks. On some occasions, stones of this description are so numerous as almost to exclude vegetation. A multiplicity of ridges and knobs of various sizes, containing rocks of this character, also make their appearance. All these formations seem to be superincumbent upon horizontal strata of secondary sandstone. But the volcanoes whence they originated have left no vestiges by which their exact locality can be determined. In all probability, they were extinguished previously to the recession of the waters that once inundated the vast region between the Alleghany and Rocky Mountains.

Of the rivers that have their courses through this section, those of most note are the Platte, the Konzas and its forks, the Arkansa, and the Canadian tributary to the Arkansa. The Platte rises in the Rocky Mountains, and after an easterly course of about eight hundred miles, falls into the Missouri, at the distance of about seven hundred miles from the Mississippi. It derives its name from the circumstance of its being broad and shoal; its average width being about twelve hundred yards, exclusive of the islands it embosoms; and its depth, in a moderate stage of water, so inconsiderable, that the river is fordable in almost every place. The main Platte is formed of two confluent tributaries of nearly equal size, called the North and South forks, both of which have their sources considerably within the range of the Rocky Mountains. They unite about four hundred miles westward from the mouth of the Platte, having meandered about the same distance eastwardly from the mountains. Besides these, {227} the Platte has two considerable tributaries, the one called the Elk Horn, entering a few miles above its mouth, and the other the Loup Fork, entering about ninety miles above the same place. The valleys of the Platte and its several tributaries are extremely broad, and in many places considerably fertile. They gradually become less fertile on ascending from the mouths of the rivers on which they are situated, till at length they exhibit an arid and sterile appearance. The alluvion of which the bottoms are composed contains a large proportion of sand, which, added to the nitrous and saline matter blended with it, occasions frequent appearances of complete barrenness. Magnesia also appears to be a component part of the soil, a quality invariably derogatory to the fertility of any soil. The valley of the Platte, from its mouths to its constituent forks, spreads to the width of ten or twelve miles, and forms a most beautiful expanse of level country. It is bounded on both sides by high lands, elevated twenty-five or thirty feet above the valley, and connected therewith by gentle slopes.

The river in several places expands to the width of many miles, embosoming numerous islands, some of which are broad and considerably extensive, and all of them covered with a growth of cotton-wood and willows. These are the only woodlands that make their appearance along the river, and in travelling westward these become less numerous and extensive, till at length they entirely disappear. Copses and skirts of woodland again present themselves in the neighbourhood of the mountains, but they are of small magnitude, and the trees they furnish are of a dwarfish growth. For a distance of nearly two hundred miles, commencing at the confluence of the North and South forks, and extending westwardly towards the mountains, the country is almost entirely destitute of woodland, scarcely a tree, bush, or even a shrub, making its appearance.

{228} The Platte is seldom navigable, except for skin canoes, requiring but a moderate depth of water, and for these only when a freshet prevails in the river. No attempts have ever been made to ascend the river in canoes for any great distance; the prevalence of shoals, and the rapidity of the current, discouraging such an undertaking. The bed of the Platte is seldom depressed more than six or eight feet below the surface of the bottoms, and in many places even less; and spreads to such a width, that the highest freshets pass off without inundating the bottoms, except in their lowest parts; the rise of the water, on such occasions, being no more than five or six feet.