230 



ROLLIN T. CHAM BERLIN 



Rockies the deformed sedimentary strata, to which one must look 

 for the record of the folding, have been completely removed from 

 large areas by the great denudation which the region has suffered. 

 In those areas the pre-Cambrian granites and gneisses now con- 

 stitute the surface formation. Over such crystalline areas folds 

 can be projected only diagrammatical] y and a large element of 

 error, or at least of uncertainty, is necessarily involved. In Middle 

 Park, sediments of Uinta age, deposited after the folded ranges 

 had been greatly eroded, now hide from view several miles of the 

 deformed terranes. Tertiary basaltic lava flows also effectively 



Mt S A VERDE 



Fig. II. — Glen wood Springs sheet (No. 13) and Grand Hogback sheet (No. 14), 

 which covers the westernmost five miles of the section. Formations: (i) pre-Cambrian 

 granite; (2) Sawatch; (3) Yule Umestone and Parting quartzite; (4) Leadville lime- 

 stone; (5) Weber and Maroon; (6) Red Beds; (7) Morrison; (8) Dakota; (9) and 

 (10) Mancos; (11) Mesa Verde. Upturned Eocene beds (mostly Wasatch) on west 

 margin of Grand Hogback sheet. 



conceal the folded structures at a number of places in the section. 

 Of these difficulties the basaltic lava covers are the least formidable, 

 owing to their lesser area and more patchy pattern, which makes it 

 possible in many places to infer the concealed structure from nearby 

 outcrops of the folded beds. But the combination of these adverse 

 conditions makes the Colorado Rocky Mountain section far less 

 satisfactory than that of the Appalachians. 



The entire cross-section of 135 miles was plotted on a scale of 

 ■3t1"8¥ oil sheets of co-ordinate paper 20 inches in length, thus 

 making each sheet cover 10 miles of section. Thirteen and a half 

 sheets thus compose the plotted section. But in computing the 

 amount of crustal shortening and the thickness of deformed shell, 

 the most easterly 3 miles of the section were excluded from con- 



