Reviews — PotoelVs Exploration of the Colorado. 369 



described in "his voyage down the river. Where the streams are 

 permanent, flood-plains or river-flats are of course found ; but the 

 intermittent torrents run through deep, steeply sloping, often im- 

 passable channels, broken by falls ; these narrow caiions being 

 sometimes inclined from the vertical, or so crookedly cut, that one 

 cannot perceive the sky looking upward from below. 



The mesas, or rocky flats along the sides of the rivers, down in 

 their gorges or caiions, seem to represent the flood-plains or river- 

 flats of other rivers, and to result from causes limiting for a time 

 the vertical erosion of the stream, which therefore acted laterally. 



Every observer who has seen the eff'ects of atmospheric erosion 

 upon stratified rocks in regions of limited rainfall with long inter- 

 missions, and many of those who have studied this agency in 

 climates where the rains are more constant, will recognize, both 

 in the author's descriptions and in his illustrations, familiar features ; 

 and there is a certain amount of simplicity about the way in which 

 he seeks to establish a somewhat mysterious classification of alcove 

 lands, cliff features, and many forms of valleys, all of which must 

 perforce have resulted from the long-continued atmospheric erosion, 

 under certain climatal conditions, of a mass of gently undulating 

 or rather more disturbed stratified rocks of different textures resting 

 upon an older fundamental series — in short, though the examples 

 are of high interest, there is nothing told of the configuration of the 

 country that would not have been expected from the combination 

 and reaction of atmospheric and geological structural conditions. 



When this great river is found running at and across the Uintah 

 mountain chain, up which it never could have climbed, yet dividing 

 it to the very heart, the inference is plain that the river existed 

 before the mountain chain did, and that the mountains are features 

 of erosion as much as the river-valley itself. Our author goes 

 further, however, and declares that the river did not cut its way 

 down through the mountains from a height of many thousand feet, 

 but that the mountains were lifted ; while the river, remaining 

 at much the same level, cleared away the obstruction by cutting 

 a canon. He likens the action to that of a log cut by a saw-mill, 

 where fresh parts of the log are continually opposed to the saw — 

 represented by the river. This action the author calls '' corrosion," 

 but while the elevation is stated for a fact, the reasons for his 

 opinion that this exceptional cause was simultaneously in operation 

 are not detailed ; and, though he admits an enormous amount of the 

 rocky surface of the country to have been denuded, he would 

 suggestively involve possible changes in the level of the sea by con- 

 traction of the ea.rth or other cosmic changes, rather than allow that 

 these great canons could have been excavated simply by the dis- 

 charge of the surface waters. Faults he has found coinciding with 

 lines of cliffs, but he traces no direct connexion between them and 

 the caiion features. 



An attempt is made to classify all the valleys by their relation to 

 the curvature or position of the strata which they traverse, which at 

 the outset must be weak, because these relations may be quite 



DECADE II,— YOL. III. — NO. VIII. 24 



