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3. Numerous flat plates of a yellow argillaceous limestone came up from the bed of the river, and were found in situ on its bank. These did not laminate, but broke across with as square a fracture as the slate. The lime was in combination,-probably an impure gypsum ; but as to that, in the absence of chemical tests, I could only judge by a sulphurous taste and smell at the fracture.
4. Everywhere in the river appeared a very remarkable conglomerate, and like the slate in exhibiting all the stages of formation. The matrix was the blue clay of the bank, the rubble was the gravel of the bottom. It was most interesting to read the history of its formation in the progressive specimens. A lump of heavy clay breaks off the shore, and is rolled over the pebbles of the bed by a rapid shallow current, which presently gives it a spherical, oval, or cylindrical contour, and studs it with a mass of small imbedded stones. As these sink deeper, the clay laps over them, and begins catching a new layer of pebbles on its fresh surface. Some less recent balls which we brought up from the bed were two feet in circumference, and little else than a mass of pebbles, cemented by hardened clay. Several were so compacted and indurated that the surface seemed nearly as homogeneous as porphyry, the matrix having become little less hard than the flintiest pebbles.
This sight staggered me in my own preconceived view, and that of many geologists, regarding the igneous origin of the harder conglomerates. From what I saw I could well conceive how the very hardest might have been the result of mere water-operations. I had regarded the pebbles of igneous origin,
found in conglomerates, as presumptive proof of the same origin for the whole mass. But the pebbles in any conglomerate might easily have been the detritus rolled from hypogene rocks down the bed of a stream with tenacious clay banks like the Republican. This view opened to me a new field of speculation upon the aqueous and igneous theories of many formations. 5. The pebbles and breccia-like detritus which inhere in the above conglomerates, are exceedingly diversified. I found among other water-worn detritus, appearing in patches between the clay and quicksand of the bottom, every possible kind of silicious material, such as agate, pure quartz crystal, smoky, rosy, and cloudy quartz, cornelian (impure), cellular quartz, and quartz united with feldspar and hornblende, or both, in all proportions and manners. One specimen of the cellular kind, associated with fibrous hornblende, was peculiarly beautiful, and resembled some of the rich auriferous specimens which I afterward found in the Colorado mines (Gregory and Bobtail lodes). All these minerals I regard as brought down by the ice and current from the head of the Republican, which, despite the United States Survey maps, is in all probability to be found as far west as Denver, and thirty miles south. They are all of Rocky Mountain formations, and resemble no outcrop in the region where I found them. 6. To a similar source may be ascribed the small particles of mica discovered in the ferruginous sand of the bed. In my field-book I wrote “must” instead of “may,” but after discoveries made it necessary for me to suspend a decision. When I reached Fort Kearney, Lieutenant Davis, then garrison commandant, showed me a specimen of mica which he had found, with many others like it, in clay beds on the
Republican, about twenty miles above our second ford. I could not gather from his description as to whether it lay apparently in situ or washed in with other debris. If the former be the true case, it opens the same interesting question regarding the aqueous or igneous origin of mica, which a little above was started about the conglomerate. If the formation of mica can be gradual and aqueous, like that of clay shale, Lieutenant Davis' specimen would be an excellent illustration of the mineral in its earlier stages. It was so soft that, although in a tabular prism and nearly quite transparent, I could scratch it almost as easily as putty, and scrape its edges into powder with my nail, and without scaling off the laminae. At first sight it appeared like calc-spar, and not till it refused to effervesce with acids did it occur to me to try its cleavage, when it laminated with ease to an indefinite thinness, each sheet showing a perfect micaceous iridescence on the surface. 7. I also found an immense boulder of almost pure feldspar, the largest mass not distinctly crystalline that I have ever seen. It was as hard as iron, of a nearly similar weight, and about three feet in circumference. 8. Near our first ford I found a small outcrop of impure shaly-brown coal, of no apparent commercial value. Butler told me that he had seen an outcropping seam of coal on the Little Blue Bluffs back of the ranch. I had no time to go and examine it, cannot therefore be certain that it is true coal,—but am inclined to believe both this and the Republican outcrop of the same period as contemporary with much which I afterward found near Denver, and which was indubitably tertiary. Of that we shall speak further. From our ford we moved down along the north bank to the intersection of the Fort Riley and Fort Kearney trail with the Republican first bottom. In some places the track was so overgrown with grass that it needed John Gilbert's eyes to find it, and considerable imagination to conceive how it could have been but a few years ago a comparatively important route from the Kaw to the Rocky Mountains. At this point a decayed old bridge of logs overhung a small stream emptying into the Republican, and just above it the beaver dams were plentier and more interesting than we anywhere saw them during our journey. We here halted for dinner; and Thompson's cows not having yet turned up with any fresh steak, we were compelled to feed on canned provisions. These disposed of, Munger, the artist, and myself continued in the buggy along a beautifully smooth, grassy bottom, with gigantic cotton-woods fringing the river all the way, to a point about a mile above the junction of White Rock Creek with the Republican. Here we picketed our horses, and prepared to camp down, building a magnificent fire of old logs, with a hollow cotton-wood for a chimney. Thompson finally appeared to tell us that the others had got tired, and were camping four miles above, also to ask if we had seen any cows. We all the more regretted to say that we had not, inasmuch as the wagons contained our whole commissariat, and we were hungry enough to have done anything for a supper except reharness and ride back four miles after we had camped down for the night. Thompson returned to the base of supplies, and we went to bed supperless. Substance being denied us, we were fain to content ourselves with shadows. Our feet lay toward the river bank, and our magnificent, though purely ornamental fire made the gigantic white trunks and grotesque gnarled branches of the cotton-woods overhanging the stream dance and flicker like ghosts in a dream. I think this was one of the noblest chiaro-oscuro effects of fire-light that I ever saw in my life. Below us murmured the river, repeating the sky’s purple twilight on its smooth depths, and glinting with diamond sparks from our flame on its fretful shallows. The air was the perfection of breathableness, softer, purer, clearer than anything east of the plains around Mount Shasta. The next morning we rejoined our companions just in time to cook our breakfast on the remains of their kitchen. I began to feel terribly sick of meat, and, in my rage for vegetables, broke my bowie-knife digging wild onions. After this exploit, costing me a splendid weapon irreplaceable short of Denver, we made a ragout of onions and salt pork, which I cannot recommend to anybody living near Delmonico's, washed our dishes in the Republican, and turned north again toward the ranch. We reached Comstock’s about two in the afternoon, with less buffalo-meat than we should have liked, but an experience of one of the loveliest and most interesting regions on the Continent; a region which the Pacific Railroad will make the most valuable farmingland between St. Louis and California.