82 REPORT UNITED STATES GEOLOGICAL SURVEY. 



shales. Noticeable throughout all formations composed of so compres- 

 sible a material as shales and marls are the vertical cleavage planes. 

 These extend through not only the shales, but implicate the beds and 

 interstrara of sandstone or other more comj)act rocks contiguous thereto. 

 In consequence of tbese already existing fissures, erosion by water and 

 frost can rapidly accomplish the work of isolation from the main bod,\. 

 Thus we find in the region of Douglas Creek groups of monuments 

 composed of shales, with cappiugs of sandstones. After the columnar 

 body has been separated from the main mass, erosion by sand and other 

 agents has full sway, and will determine the detail features of the in- 

 dividual monument. Although more rapidly formed, perhaps, than the 

 monuments of the Garden of the Gods, these also have a shorter exist- 

 ence. Atmospheric influences will soon succeed in crumbling down the 

 frail support, and the protecting sandstone will no longer be sustained. 



With this, the occurrence of Wasatch beds in my district is exhausted. 

 It is, as that of the preceding ones, but limited. In a great measure 

 this is owing to the regularity of the stratigraphical conditions. Ab- 

 sence of widely-spread erosion from the surface downward causes the 

 Wasatch to remain bidden from sight. 



Green River Group. — Perhaps the best exposure of this group within 

 the limits of our district may be found on the steep face presented by 

 the Book Cliffs just north of the Grand Kiver. From the crest of the 

 cliffs to the precipitous edge facing toward the Grand the fall of the 

 summit is about 500 feet, but there it reaches nearly 3,000 feet within a 

 horizontal distance of less than two miles. On this face the best sec- 

 tion of the members composing the group may be seen. Regarding 

 the eastern half of the Green Kiver area from a topographical stand- 

 point, we observe a quite curious case. The section lying between 

 White River and the Grand is essentially a plateau, ascending gently 

 toward the south. For about twenty -five miles the rise south of White 

 River is a regular, gentle one. Streams, belonging to thePi ce-auce drain- 

 age cut through the soft-yielding shales, leaving uniform ridges be- 

 tween them. At that distance, 2,800 leet above White River, the divide 

 between this and the Grand is reached. Although no perceptible 

 change takes place in the stratigraphical arrangement of the strata, we 

 find that suddenly the waters flow in an opposite direction into the 

 Grand. They flow in deep, narrow caiions, that are almost inaccessible. 

 As they continue their southward course, the walls of the caiions be- 

 come higher and higher. More correctly speaking, the tops of the en- 

 closing walls retain very nearly the same level, while the stream-bed is 

 worn deeper into the strata over which it flows. The southern edge of 

 the northward sloping plateau reaches to within three miles of the 

 Grand. Where the tributaries of that stream leave their caiions, the 

 latter have walls 3,000 feet in height, while the plateau edge is but 400 

 feet lower than the divide between the two rivers. We have, therefore, 

 in this instance, one of those peculiar cases which could be explained 

 by the same assumption that Professor Powell claims for so many of 

 his observations in the region of the Colorado River. This expUina- 

 tion asserts that during the period in which flowing water followed ap- 

 proximately the same courses as today, the southern edge of this pla- 

 teau would have been elevated ; that the erosive power of the water 

 was more than adequate to the rapidity of the elevation, and that, in 

 consequence, the water maintained its own former level, while the caiion 

 walls grew higher and higher. No doubt this view is a very ingenu- 

 ous one, and, if applicable anywhere, it wouM seem that here in these 

 soft shales there was an excellent opportunit}' for its consummation. 



