402 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



At Utah line the boundary between Utah and Colorado is marked 

 by a white line running- up the face of the cliif. 



A few miles further east, after passing round a northward projecting 

 point of the cliffs, one can distinguish along the banks of the river and 

 projecting above its surface in midstream, rounded knobs of Archean 

 rocks, blackened, polished, and singularly channeled by the action of 

 the water. These rocks form apparently an east and west ridge in the 

 line of the monoclinal fold, which the road now follows for some dis- 

 tance on a tangent. 



Just before reaching Ruby an excellent section of the monoclinal 

 fold maybe seen on the north side of the river, where a small tributary 

 ravine is cut along its axis. 



The road now passes beyond the fold into the gray sandstones and 

 intercalated shales of the Jurassic and Dakota Cretaceous, in which 

 the effects of undermining by the action of the stream are well displayed. 

 It soon leaves the valley of the Grand river, passing up a tributary 

 ravine, through a tunnel in Dakota sandstone, and out on to the broad 

 valley of Cretaceous shales again. Twelve miles (19 km.) distant, form- 

 ing the southern boundary of this valley, are the Little Book cliffs,* 8 

 the eastern continuation of the line of cliffs which has been followed 

 from Utah. It is formed here entirely of Cretaceous beds, the over- 

 lying Tertiary beds forming a second line of cliffs farther back, trend- 

 ing to the northeast, for all the beds are now commencing to rise to the 

 east on the west Hanks of the Rocky mountains. 



The clay valley is followed to Grand Junction, a growing town that 

 is now becoming prominent for the excellent quality of its fruits which 

 have been raised by its citizens on the neighboring mesas under the 

 beneficent intluence of irrigation. 



