These features are well shown in Plate II, where the Waterpocket flexure is contrasted with the Henry Mountain arches. CHAPTER V. LAND SCULPTURE. The Basin of the Colorado offers peculiar facilities for the study of the origin of topographic forms, and its marvelous sculpture has excited the interest of every observer. It has already made notable contributions to the principles of earth sculpture[5], and its resources are far from exhausted. The study of the Henry Mountains has not proved entirely unfruitful, and for the sake of showing the bearing of its peculiar features upon the general subject, I shall take the liberty to restate certain principles of erosion which have been derived or enforced by the study of the Colorado Plateaus. Footnote 5: Geology of the “Colorado Exploring Expedition”, by J. S. Newberry, p. 45. “Exploration of the Colorado River of the West”, by J. W. Powell, p. 152. “Geology of the Uinta Mountains”, by J. W. Powell, p. 181. “Explorations West of the 100th Meridian”, Vol. III, Part I, by G. K. Gilbert, pp. 67 and 554. “The Colorado Plateau Region” in American Journal of Science for August, 1876, by G. K. Gilbert. A portion of the last paper is repeated, after modification, in the first section of this chapter. I.—EROSION. The sculpture and degradation of the land are performed partly by shore waves, partly by glaciers, partly by wind; but chiefly by rain and running water. The last mentioned agencies only will be here discussed. The erosion which they accomplish will be considered (A) as consisting of parts, and (B) as modified by conditions. A. PROCESSES OF EROSION. All indurated rocks and most earths are bound together by a force of cohesion which must be overcome before they can be divided and removed. The natural processes by which the division and removal are accomplished make up erosion. They are called disintegration and transportation. Transportation is chiefly performed by running water. Disintegration is naturally divided into two parts. So much of it as is accomplished by running water is called corrasion, and that which is not, is called weathering. Stated in their natural order, the three general divisions of the process of erosion are (1) _weathering_, (2) _transportation_, and (3) _corrasion_. The rocks of the general surface of the land are disintegrated by _weathering_. The material thus loosened is _transported_ by streams to the ocean or other receptacle. In transit it helps to _corrade_ from the channels of the streams other material, which joins with it to be transported to the same goal. _Weathering._ In weathering the chief agents of disintegration are solution, change of temperature, the beating of rain, gravity, and vegetation.