649. Poa serotina, Ehrh. 1873. July, August. Pembina. Turtle Mountain. *650. Festuca borealis, Mert. *651. Festuca ovina, L. 652. Bromus ciliatus, L. 1873. August. Mouse River. 1874. August. West of Frenchman's Creek. 653. Phragmites communis, Trin. 1873. August. Prairie, on borders of little pools. *654. Lepturus paniculatus, Nutt. 655. Triticum caninum, L. 1873. August. Near Turtle Mountain, in thickets. 656. Triticum repens, L. 1874. July. Frenchman's Creek. *657. Triticum strigosum, Steud. 658. Hordeum jubatum, L. 1873. July. Pembina, on prairie. 1874. July. Missouri River. 659. Hordeum pratense, Huds. 1874. August. West of Frenchman's Creek. 660. Elymus Canadensis, L. 1873. August. Turtle Mountain, thickets. *661. Elymus Canadensis, var. glaucifolius. 662. Elymus Sibiricus, L. 1874. August. Rocky Mountains. 663. Elymus Virginicus, L. 1873. August. Near Turtle Mountain. *664. Danthonia spicata, Beauv. #665. Avena striata, Mx. 666. Aira cæspitosa, L. 1874. August. Base of Rocky Mountains. 667. Phalaris arundinacea, L. 1873. July, August. Pembina. Turtle Mountain, thickets. 1874. July. Frenchman's Creek. *CGS. Hierochloa borealis, R. & G. 669. Beckmannia erucaformis, Host. 1874. July, August. Missouri River. Frenchman's Creek. *670. Panicum pauciflorum, Ell. 671. Panicum virgatum, L. 1873. August. Mouse River. *672. Andropogon furcatus, Muhl. 673. Andropogon scoparius, Mx. 1873. September. Mouse River, dry prairie. 674. Equisetum arvense, L. EQUISETACEÆ. 1873. July. Pembina. *675. Equisetum hyemale, L. *676. Equisetum lævigatum, Braun. *677. Equisetum limosum, L. 678. Equisetum robustum, Braun. 1874. June. Missouri River. FILICES. *679. Polypodium vulgare, L. *684. Cystopteris bulbifera, Bernh. LYCOPODIACEÆ. *689. Lycopodium complanatum, L. *690. Lycopodium lucidulum, Mx. 691. Selaginella rupestris, Spreng. 1874. August. Base of Rocky Mountains, and almost any where eastward, in some places covering the face of the country and forming much of the sod on sterile hills. 692. Evernia alpina. LICHENES. 1874. August. Rocky Mountains. ART. XXXV.-ON SOME STRIKING PRODUCTS OF EROSION IN COLORADO. BY F. M. ENDLICH, S. N. D. During the progress of the geological and geographical survey of Colorado, under the direction of Dr. F. V. Hayden, every portion of that interesting State was explored. Numerous data were obtained, important not only to the geologist, but furnishing ample material to the artist, enjoyment to the traveller. Few States, perhaps, are so well favored by nature as Colorado. Some of the grandest mountain scenery within the United States is there to be found; mineral wealth is treasured up within the earth's interior. Farms and meadow land, rich in their yield, are scattered throughout the State; and, again, the traveller may visit within this State regions that will forcibly remind him of the Sahara. Now that its exploration is finished and its features throughout are thoroughly known, we are enabled to present more connected discussions upon the characteristic forms there observed. No group of forms, probably, is so unique as that showing numberless changes produced by the sculpturing hand of nature. Erosion, its artistic agent, has furnished us, in Colorado, with results at once striking and singularly beautiful in detail. To these the following pages shall be devoted. Fully aware that no pen-picture can convey an adequate idea of the subject, I may still hope that an accurate description may be of some service to those seeking information thereupon. For many years the classical region of Monument Park has been known. The singular shapes of its rocks and brilliancy of their colors have given a justly earned celebrity to the place. Since that time many other localities have been discovered, some of them even surpassing the former in grandeur and beauty. Lying farther toward the interior of the State, the regular tourist has not yet reached these spots, and the revelation of their wonders has thus far been made to a favored few only. In the course of years, no doubt, as communications shall be more completely established, these places, too, will be visited, and will elicit admiration equal to that now bestowed upon Monument Park. Until that time arrives, however, descriptions must be accepted which cannot. possibly do justice to the subject. EROSION. Two classes of erosive agents may be distinguished, chemical and physical. Of these, the former has but one function, the latter two. Chemical agents produce such changes in the rock as may, and most frequently do, result in its partial or complete decomposition. This decomposition is the destruction of original and the consequent formation of new compounds. Very often it is accompanied by an increase of volume, whereby the original molecular cohesion is disturbed. On the other hand, it may result in the removal of certain constituents, thus producing an effect directly inverse to the former. By either of these processes, the mass is disturbed in such a manner as to render it less impregnable to the attacks of physical erosives. Although we cannot have, therefore, a truly chemical erosion in all instances, we are justified in using the term, because the chemical action is the immediate means by virtue of which the mechanical work may be accomplished. Most prominent among the chemical agents facilitating mechanical erosion are water, either pure or charged with various gases, and growing vegetation. Minerals like feldspar, anhydrite, and others absorb water, and are changed into caolinite and gypsum respectively. Both of these secondary products are less able to withstand erosion than the original compounds. This represents the case where changes of chemical composition prepare the material in such a manner as to offer the least resistance to physical erosives. Water charged with gases, more particularly carbonic acid gas, will dissolve certain compounds readily and carry away portions thereof in solution. Hot and cold water, pure, will act in the same manner, but to a less degree. Growing vegetation will chemically absorb certain ingredients of rocks upon which its roots may be resting, thus either directly removing small quantities of the material or changing its chemical composi tion. This erosive action by vegetation becomes insignificant, however, when compared with the far superior physical force growing plants exhibit. Gases contained in the atmosphere have some effect upon rocks of varying constitution, but frequently one that tends rather to preserve than to destroy the material acted upon. Oxydation is the most widely distributed result of such influence. Most prominent among the agents of physical or mechanical erosion is the action of water, wind, and growing vegetation. Again, we find that by vegetation the subsequent absolute removal of material is prepared. The growth of roots in minute crevices of rocks may frequently result in a disruption of the cohesion, thus either directly removing a fragment or placing it into such a position as to make its removal imminent. To every one is known the enormous expansive power of growing roots, and it will readily be seen how very severely a large mass of them may affect a rock that has, for instance, the physical constitution of a sandstone. Flowing water, with or without sand and detritus in suspension, is one of the most directly acting agents, and is productive of results upon a grand scale. Analogous thereto, though more restricted in occurrence, is the action of moving ice. Precipitated water presents results similar to the foregoing, but on a small scale. Water entering fissures and seams, or saturating porous rocks, severely affects them by expansion incident upon freezing. Within certain classes of rocks, this process, preparatory to the final removal of material, is one of great importance. Not only are those that may be regarded as mechanical deposits thereby affected, but also the crystalline aggregates. Water entering minute openings between the cleavage-planes of crystals will gradually produce a separation so great as to render the original position of the crystal no longer tenable. This mode of separation is analogous, in its results, to the effects produced by growing roots. For flowing and precipitated water is reserved the ultimate transportation of such loosened material from its original place of occurrence. Wind, finally, is the last of the important agents of erosion. By its force, small, loosened particles are removed and are carried away. Sand carried before the wind is capable of producing very marked results. By the frequent repetition and violence of the concussions caused by grains of sand striking against some fixed obstacle, a type of erosion is produced that may be regarded as unique in its detail characteristics. While the cutting action of the sand detaches fragments of the rock, the wind rapidly carries them off, thus ever offering fresh surfaces to the attacks of the rapidly abrading material. The comparatively small amount of work that is apparently accomplished by this powerful factor of erosive agents may be due to the fact that peculiar positions of the eroded material are required. Unless these conditions be complied with, the sand will speed harmlessly upon its way, or produce such results as furnish no adequate examples of its power. Reviewing, briefly, the characteristics resulting from the various methods of erosion, we observe that certain analogous physical causes produce essentially the same forms. Water acts as a solvent agent upon many of the minerals constituting rocks. Although the quantity of mineral matter taken into solution by pure water is, as a rule, indefinitely small, the presence of carbonic acid gas makes a great difference in its solvent power. Frequently exposures of limestones may be seen, exhibiting a minutely corrugated surface. Gypsum is affected in the same way by chemical aqueous erosion. Admixtures of silex and clay in either limestones or gypsum produce definite results, which lead to a recognition of their presence. Although the chemical erosion caused by growing vegetation in the aggregate will show extensive results, its direct evidence is not very manifest. Owing to the distribution of minute root-fibers, their chemical action is spread so uniformly that it can be recognized as such only in rare instances. Perhaps the most universally observed products of erosion are those shaped by flowing water. Channels are worn into yielding rocks, rough places are smoothed, soft inclosures in hard rocks are removed, and, throughout, the outlines are modified. These results are, in a great measure, dependent upon the quantity and quality of the material which |