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

by Edwin James; Stephen H. Long; Thomas Say

2d. Argillaceous, or Gray Sandstone—Overlays the red, conforming to it in the inclination of the strata, occurs principally near the primitive; contains coal and iron.

3d. Greenstone and Graystone[83]—Of an imperfectly columnar structure, resting on the argillaceous sandstone.

4th. Amygdaloid—Sometimes containing argil, and sometimes hornblende, occurs with the greenstone about the sources of the Canadian river, constituting with the former the newest fletz trap formation.

5th. Sand and Gravel—Accompanying the sandstones and extending over the great desert, but rarely found resting on the trap rocks.

The sandstones being entirely mechanical aggregates, consisting of rounded fragments of rocks formerly constituting a part of the primitive mountains, would seem to have been deposited at a very remote period, when the waters of the primeval ocean covered the level of the great plain and the lower regions of the granitic mountains.

Subsequent to the deposition of the horizontally stratified rocks, the position of these in relation to the primitive, has been somewhat changed either by the action of some force beneath the primitive rocks, {295} forcing them up to a greater elevation than they formerly possessed, or by the sinking down of the secondary, produced by the operation of some cause equally unknown. Without supposing some change of this kind, how can we account for the great inclination of the margin of the sandstone rocks which is found resting against the granite almost perpendicularly? Nearly contemporaneous to this change, was the retiring of the sea, and the formation of the trap rocks. The beds of loose sand and gravel which are still constantly accumulating, have been formed in part from the disintegration of the sandstones and puddings, and partly by the action of those currents of water which are constantly bringing down small fragments from the primitive rocks, and depositing them in the plains.

The absence of any formation of limestone is a distinguishing characteristic of the country under consideration. A traveller to the upper part of the Missouri mentions "calcareous and petrosiliceous hills," as existing in the coal districts on that river. But in ascending the Platte from its confluence with the Missouri to the mountains, we saw not a single fragment of limestone. Small veins of carbonate of lime crystallized in the usual form, are met with in the argillaceous sandstone of the Arkansa, also the sulphate in small quantities. Gypsum is very abundant on the Canadian river, at a distance of three or four hundred miles from the mountains. It is disseminated in veins and thick horizontal beds in the red sandstone. The extent and thickness of these horizontal beds are, perhaps, such as would justify the appellation of stratum, but as it is not met with in great quantities, except in connection with the sandstone, with which it often alternates, it may with propriety be considered a subordinate rock.

Rock Salt.—This substance has often been said to exist in some part of upper Louisiana, in the form of {296} an extensive stratum: we have met with salt among the natives in masses of twenty or thirty pounds weight. The interior of these masses when broken, presented a crystalline structure, being made up of incomplete cubic crystals variously grouped together. On one of the surfaces, which had probably been the one in contact with the ground or rock on which the salt had rested, a considerable mixture of red sand was discoverable. These masses had apparently been produced by the evaporation, during the dry season, of the waters of some small lake. The whole country near the mountains abounds in licks, brine springs, and saline efflorescences, but it is in the neighbourhood of the red sand-rock before mentioned, that salt is met with in the greatest abundance and purity. The immediate valley of the Canadian river in the upper part of its course, varies in width from a few rods to three or four miles, but it is almost invariably bounded by precipices of red sand-rock, forming "the river bluffs." In the valley between these, incrustations of nearly pure salt are often found, covering the surface to a great extent, in the manner of thin ice, and causing it to appear when seen from a distance, as if covered with snow.

Most of the remarkable formations of rock-salt hitherto known, have been found in the stratum denominated "the lowest red sand rock," which appears to correspond in character, position, &c. with the sandstone above mentioned. Rock salt is found in connection with this sandstone in Cheshire, and at Northwich and Droitwich, in England, at Cardona in the province of Catalonia in Spain, and at the base of the Carpathian mountains in Moldavia and Poland. In Peru it is accompanied by sandstone and gypsum.

Accident, or further examination, it is probable, may hereafter bring to light those extensive beds of {297} this substance, which there is reason to believe exist in the neighbourhood of the Rocky Mountains. The briny character of those great streams, the Arkansa and Red rivers, flowing over the red sandstone formation, and receiving from it the peculiar character and colour of their waters, affords sufficient evidence of the existence of such beds, and the greatness of the quantity washed away in any given time, would lead to the conclusion, that they must be of vast extent. By the analogy of other rock salt formations apparently similar in character, we should be instructed to search for these beds in depressed situations and basin-shaped cavities, whose contents had not been worn down and removed by the currents of water.