cataract, eight, ten, even seventeen thousand feet in height. These floods of cold wind find their appropriate channels in the characteristic _canons_ which everywhere furrow the whole Rocky-Mountain system to its very base. Most of these are exceedingly tortuous, and the descending winds, during their passage through them, acquire a spiral motion as irresistible as the fiercest hurricane of the Antilles, which, moreover, they preserve for miles after they have issued from the mouth of the _canon_. Every little cold gust that I observed in the Colorado country had this corkscrew character. The moment the spiral reaches a loose sand-bed, it sweeps into its vortex all the particles of grit which it can hold. The result is an auger, of diameter varying from an inch to a thousand feet, capable of altering its direction so as to bore curved holes, revolving with incalculable rapidity, and armed with a cutting edge of silex. Is it possible to conceive an instrument more powerful, more versatile? Indeed, practically, there is no description of surface, no kind of cut, which it is not capable of making. I have repeatedly seen it in operation. One day, while riding from Denver to Pike's Peak, I saw it (in this instance, one of the smaller diameters) burrow its way six or seven feet into a sand-bluff, making as smooth a hole as I could cut in cheese with a borer, of the equal diameter of six inches throughout, all in less time than I have taken to describe it. Repeatedly, on the same trip, I saw it gouge out a circular groove around portions of a similar bluff, and leave them standing as isolated columns, with heavy base and capital, presently to be solidified into just such rock pillars as throng the cemeteries or aid in composing the strange architectural piles mentioned above. Surveyor-General Pierce of Colorado, (a man whose fine scientific genius and culture have already done yeoman's service in the study of that most interesting Territory,) on a certain occasion, saw one of these wind-and-silex augers meet at right angles a window-pane in a settler's cabin, which came out from the process, after a few seconds, a perfect opaque shade, having been converted into ground-glass as neatly and evenly as could have been effected by the manufacturer's wheel. It is not a very rare thing in Colorado to be able to trace the spiral and measure the diameter of the auger by rocks of fifty pounds' weight and tree-trunks half as thick as an average man's waist, torn up from their sites, and sent revolving overhead for miles before the windy turbine loses its impetus. The efficiency of an instrument like this I need not dwell upon. After some protracted examination and study of many of the most interesting architectural and sculpturesque structures of the Rocky-Mountain system, I am convinced that they are mainly explicable on the hypothesis of the wind-and-silex instrument operating upon material in the earthy condition, which petrified after receiving its form.