think such an agency inadequate to the large and largely varied excavations which have taken place in the Colorado drift-bed, need only witness a whirlwind like those which it was my fortune to encounter both along the Platte and in the mountains, to make their minds entirely easy on the subject. There is no achievement of force beyond the capability of a Rocky Mountain tornado. It would take too long to investigate all the meteorological conditions which underlie this fact; but one abundant reason exists in the contour of the mountains, and their relative position with the Plains. The Plains, over their whole sandy surface, compose a vast radiator; discharging immense quantities of heat into the atmosphere during the entire sunny period of every day.

From dawn till night-fall the superjacent stratum of air undergoes constant rarefaction, and, as it ascends to meet the westerly current, is progressively carried into the higher mountain region adjacent. Here it parts with a portion of its caloric, but is pressed back by continuous rarifications from below, until with darkness the process stops, at a state of things like the following: an immense body of air condensed among the mountains, but every moment growing colder and heavier, a comparative vacuum existing immediately over the Plains below. The result is an immediate wind-cataract, falling from the height of about twenty thousand feet. But this fall does not make a straight plunge, like Niagara. It descends not over a precipice, but through a chasm. One characteristic of the Rocky Mountains is its system of vast indentations, cutting through from the top to the bottom of the range. Some of these take -he form of funnels, others are deep, tortuous galle

ries, known as passes or cañons; but all have their openings toward the Plains. The descending masses of air fall into these funnels, or sinuous canals, as they slide down, concentrating themselves and acquiring a vertical motion. By the time they issue from the mouth of the gorge at the base of the range, they are gigantic augers, with a revolution faster than man's cunningest machinery, and a cutting edge of silex, obtained from the first sand-heap caught up by their fury. Thus armed with their own resistless motion, and an incisive thread of the hardest mineral next to the diamond, they sweep on over the Plains, to excavate, pull down, or carve into new forms whatever friable formation lies in their way. I can give no better idea of the efficiency of this instrument than by citing a few examples from actual experience. First, as to carrying capacity. That portion of the track between Denver and Pike's Peak which lies across the open Plains is every year repeatedly buried out of sight under gravel large enough to make it seem macadamized, blown from the foot-hills, a distance of several miles, by the ordinary winds of the region. It is no It is no uncommon occurrence to see large trees in the path of the whirlwind torn up by the roots, and carried, revolving as they go, a distance of several miles into the Plains. Stones of many pounds' weight are sometimes served in the same way, seeming to be retained in the vertical whirl with as much ease as a cloud of dust or a splinter of wood.

Second, as to the force of the wind-auger. I myself have seen a hole bored into a Colorado sand-bluff, several feet deep, and of sufficient diameter to admit one's arm, by a small spiral current which rose on a

comparatively calm day, and without any general atmospheric perturbation. The work was done in a few seconds; and no machinery could have accomplished it more neatly. Mr. Pierce informed me of much larger excavations which he had seen effected with equal dispatch. But the account of his from which I gained my best idea of the exact composition and operation of the wind-and-silex auger, was to the effect that on a certain occasion, when he was stopping at a settler's cabin during the prevalence of one of these mountain whirlwinds, a spiral current, laden with sand-grains, impinged against one of the windowpanes, and, after a few moment's revolution, left it as perfect a piece of ground glass as could be made. by a manufacturer of lamp-shades.

It is to the agency of this wind-and-silex auger that I ascribe all the mimetic formations of the Colorado foot-hills. Though a tool of tremendous force, it possesses a flexibility which enables it to accept any curved path; and this is an essential requisite of the instrument which can create such sculptures. It is a far more delicate tool than running water; for it acts by mechanical force alone, while water chemically decomposes the rocks whose surface it is abrading, and crumbles them to pieces while it is channeling their outsides. I consider the wind-and-silex auger the cleanest tool that Nature works with. It corresponds to man's highest advance in a similar direction, -the lathe for turning eccentric surfaces. The work that it does, no other agency could do; and we are thus indebted for one of the most characteristic features of our contemporary geology to a force scarcely noticed in its dynamics.

About four o'clock in the afternoon we came into a

narrow valley between perpendicular uplifts of red and white argillaceous sandstone, which towered, bare as a house-wall, to the height of three or four hundred feet. The effect of the sunlight on these brightly colored precipices was splendid in the extreme. They guarded the sides of our narrow avenue for a distance of three or four miles, and only left us at the edge of the little settlement of Colorado City.

We drove to the one place of entertainment which the town possessed,-a small wooden structure, whose title of the El Paso House was an indication of our approach toward Mexican boundaries and Mexican manners. The latter fact was abundantly attested by the slovenliness with which the house was managed, the discomfort of its rooms, and the melancholy recklessness of its table.

But we were in no mood to grumble, having such food for the eyes and head as dispensed with the necessity of other aliment. The dozen buildings of which Colorado City is composed, lie in a sand plain at the base of the foot-hills which wait upon Pike's Peak. The grand old mountain itself projects its head of glittering snow, through a gap in the nearer ranges which surround it, to a height and loneliness. which almost tire imagination. Its altitude is very differently estimated, but cannot vary much from sixteen thousand feet. The best view of it is not from the base of its foot-hills at Colorado City, for its full proportions are veiled at that point by intermediate ranges, but far out on the Plains, east of the town, where for more than a hundred miles the emigrant sees it standing, a solitary beacon, with every detail melted into one heaven-piercing cone. How prominent an object it is, may be inferred from the fact

that it gave its name to this entire region,-the man who came to the Colorado mines being a "Pike'sPeaker," though his nearest lodes were situated a hundred miles from that mountain by the shortest

access.

A mountain which I admire more than Pike's Peak (or at least the Colorado City view of it), is the grand Cheyenne, which rises a little further south, and is plainly visible at the rear of the El Paso House, from base to dome. Its height is several thousand feet less than Pike's; but its contour is so noble and so massive that this disadvantage is overlooked. There is a unity of conception in it unsurpassed in any mountain I have seen. It is full of living power. In the declining daylight, its vast simple surface became the broadest mass of blue and purple shadow that ever lay on the easel of Nature.

Having refreshed ourselves with a good night's rest, in which fatigue met fleas and came off conqueror, we took an early start from the El Paso, to examine the natural features of this most interesting region.

Our first visit was paid to a shale-bed on the Fontaine qui Bouille, in which I had heard through Mr. Pierce of the discovery of interesting tertiary remains.

Mr. Garvin, a man of varied experience as sailor, hunter, miner, and merchant, who had finally settled down among the Rocky Mountains, and was conducting a Colorado City branch of George Tappan's house, accompanied us in our examination, and much assisted us by his knowledge of localities. We were joined by another gentleman of the same name, but no relationship with the former, (a singular coincidence in so small a directory!) a Dr. Garvin, whose