PHYSICAL FEATURES OF COLORADO VALLEY. 537 



seen in the Brown Cliffs and the upper portion of the Book Cliffs. 

 In the last-mentioned escarpment the harder beds are underlaid hy 

 soft, bluish shales, which appear below in the beautifully-carved but- 

 tresses. 



In the Orange Cliffs there are a thousand feet of homogeneous 

 light-red sandstone, and this is undei-laid by beds of darker red, choco- 

 late, and lilac-colored rocks, very distinctly stratified. The dark-red 

 rocks are very hard, the chocolate and lilac are very soft, so below we 

 have terraced and buttressed walls and huge blocks scattered about, 

 which have fallen from the upper part of the escarpment. The homo- 

 geneous sandstone above is slowly undermined so slowly that, as the 

 unsupported rocks yield to the force of gravity, fissures are formed 

 parallel to the face of the cliff. Transverse vertical fissures are also 

 formed, and thus the wall has a columnar appearance, like an escarp- 

 ment of basalt, but on a giant scale ; and it is these columns that 

 tumble over at last, and break athwart into the huge blocks which 

 are strewed over the lower terraces. 



The drainage of an inclined terrace is usually from the brink of the 

 cliff toward the foot of the terrace above, i. e., in the direction of the 

 dip of the strata. As the channels of these intermittent streams ap- 

 proach the upper escarpment, they turn and run along its foot until they 

 meet with larger and more permanent streams, which run against the 

 dip of the rock in a direction opposite the course of tlie smaller chai> 

 nels, and these latter usually cut either quite through the folds, or at 

 least through the harder series of rocks which form the cliffs. 



In some places the waters run down the face of the escarpment, 

 and cut nai*row canons, or gorges, back for a greater or less distance 

 into the cliffs, until what would, otherwise, be nearly a straight wall, 

 is cut into a very irregular line, with salients and deep reentering 

 angles. 



These canons which cut into the walls also have their lateral canons 

 and gorges, and sometimes it occurs that a lateral canon from each of 

 two adjacent main canons will coalesce at their heads, and gradually 

 cut oft* the salient cliff from the ever-retreating line. In this way 

 buttes are formed. The sides of these buttresses have the same 

 structural characteristics as the cliffs from which they have been cut. 

 So the buttes on the plains below the Orange Cliffs are terraced and 

 buttressed below, and fluted and columned above. Often the upper 

 parts of these buttes are but groups of giant columns. 



The three lines of cliffs, which I have thus described, have been 

 traced to the east but a few miles back from the river. The way in 

 which they terminate is not known ; but, fi'om a general knowledge 

 obtained from a hasty trip made through that country, it is believed 

 tlvat they are cut off by a system of monoclinal folds. To the west 

 they are knowni to gradually run out in plateaus and mountains, which 

 have another orographic origin. 



