248 ROLLIN T. CHAM BERLIN 



GENERAL DISCUSSION AND CONCLUSIONS 



These studies would seem to show that the Colorado Rockies 

 differ in several notable respects from the folded Appalachians of 

 Pennsylvania. 



1. They have suffered, in the first place, much less horizontal 

 compression. From the Great Plains to the Uinta Basin, 140 

 miles of country were compressed into 132 miles, thus involving a 

 shortening of only 8 miles, while west of Harrisburg alone 81 miles 

 of strata were squeezed into 66 miles of present Appalachians, which 

 means a shortening of 15 miles in this much narrower belt. This 

 does not include the folding in the metamorphic belt east of 

 Harrisburg. 



2. A much thicker shell seems to have been involved in the 

 Rocky Mountain diastrophism than was actively deformed in the 

 Appalachian folding. The apex of the Pennsylvania Appalachian 

 wedge was but 32 miles below the surface, while the roots of the 

 Gore Range reached a depth of 87 miles and the plateau tract near 

 Glenwood Springs had a depth of 107 miles. 



3. Vertical lifting and plateau-forming movements have been 

 more pronounced in the Rockies than in the Appalachians. This 

 is indicated both by the outcome of this analysis, and also by the 

 present high altitude of the Colorado Front Range peneplain, 

 though the elevation of the latter, to be sure, came long after the 

 principal folding, which is the basis of this investigation. 



4. The formation of the Colorado Rockies was accompanied by 

 much more vulcanism than the formation of the Appalachians. 



These conclusions lead naturally onward to certain additional 

 deductions and further applications. These specific results confirm 

 the principle that there is an inherent relation between thickness 

 of shell actively involved and intensity of deformation. This 

 justifies the conclusion that mountain ranges displaying intense 

 folding, thrust faulting, and dynamic metamorphism resulting from 

 extreme horizontal compression are associated with a thin, shallow 

 shell. This thin, movable shell, which has been greatly folded and 

 faulted, shears upon the less yielding base beneath it. Ranges of 

 this sort are the Appalachians and presumably the Jura, Alps, 

 Scottish Highlands, Scandinavian chain, and others of great short- 



