2G4 GEOLOGICAL EXCURSION TO THE ROCKY MOUNTAINS. 



of volcanic origin, stand near the Canadian boundary. The underly- 

 ing strataare chiefly Cretaceous and Tertiary, and in general these 

 have been reduced to an even surface. In a few districts, however, 

 local causes have accelerated corrosion, causing the sculpture of shaly 

 beds into the picturesque " Bad lands." On the outward journey the 

 Great plains are traversed in North Dakota and the eastern half of 

 Montana; on the return journey, from Denver to the Missouri river. 

 The branch route to the Colorado canyon traverses the western edge of 

 the plains from Denver to Las Vegas. 



The Cordilleran region includes the Rocky mountains, the Plateau 

 region, the Great basin, the Snake River plain, the Siena Nevada, 

 and a number of more westerly divisions beyond the limits of the 

 journey. 



The name Rocky mountains is applied in Colorado and northern New- 

 Mexico to the complex mountain chain lying between the Great plains 

 and the Plateau region, and in Montana and northern Wyoming to the 

 mountain chain between the Great plains on the east and the Snake 

 River plain on the west. In central Wyoming there is a discontinuity 

 the mountain chain being interrupted by an arm of the Plateau region 

 known as the Laramie plain. The Rocky mountains of Colorado con- 

 stitute the greatest mountain mass of the United States, although a 

 few peaks in the Sierra Nevada exceed them in height. Their principal 

 uplift took place at a later date than that of the Appalachian Mountains 

 and they are far more rugged. The type of Structure involves Jess of 

 closely compressed folding, and faulting has played a more prominent 

 part in producing their present relief. The nucleal rocks range from 

 crystalline schists through the Paleozoic Rfesozoie strata appear abou* 

 the Hanks, sharing in the uplift, and lacustrine beds of Oenozoic date 

 rise against the bases on all sides and are to be discovered in most' of 

 the mountain valleys. In various places, and especially toward the 

 south, there are great masses of volcanic rocks, and dikes abound in 

 all parts. The Rocky mountains of the northern group are of similar 

 type, and also consist of lofty ami rugged ranges. From these two 

 masses tlow the longest rivers of the country. The Mississippi-Mis 

 soun rises in the northern chain, receives many affluents Iron/ the 

 southern, and flows southward to the Gulf of Mexico. The length of 

 its main line is 4,900 miles (7,080 km.). The Columbia, rising in the 

 nor hern chain reaches the Pacific Ocean after flowing 1,4,K) nn.es 



( T V no , S ° Utbern ( ' haln lik( ' wise se,,ds «» Ki ° Gtonde 2,000 

 nules (3,200 km.) to the Gulf of Mexico, and is drained on the wes bv 



he tributaries of the Colorado, whose waters flow 1,300 utiles (2 100 



fan.) to the Gulf of California. On the outward journey the n>ut<: lie 



along the mountains of the northern chain from Cinnabar to Poeate lo" 



on the return journey it lies among the Rocky mountains of Colorado' 



