234 ROLLIN T. CHAMBERLIN 



No. lo. Castle Peak sheet Miles 



Length following base of Dakota sandstone lo . 20 



Present horizontal length 10.00 



Shortening .20 



No. 1 1 .' Gypsum sheet 



Length following base of Dakota sandstone 10.235 



Present horizontal length 10.00 



Shortening .235 



No. 12. Dotsero sheet 



Length following base of Dakota sandstone 10 . 29 



Present horizontal length . ; 10.00 



Shortening .29 



No. 13. Glenwood Springs sheet 



Length following base of Dakota sandstone 10.265 



Present horizontal length . . 10.00 



Shortening . . ... . . . . . . . . .256 



No. 14. Grand Hogback sheet 



Length following base of Dakota sandstone 6 . 20 



Present horizontal length 5 • 00 



Shortening . . i . 20 



Summation: Entire Lyons-Glenwood Springs section 



Total original length (base of Dakota sandstone) . . . 140 . 69 

 Present horizontal length 132.00 



Total shortening 8 . 69 



According to these measurements, the lateral thrusting which 

 produced the Colorado Rockies compressed 140. 69 miles of country 

 into 132 miles, thus bringing two points on opposite sides of the 

 folded belt 8 miles closer together than they were before the fold- 

 ing commenced. A crustal shortening of 8 miles distributed 

 throughout a belt of originally 140 miles in breadth does not indi- 

 cate very intense horizontal thrusting. The horizontal compression 

 was much less than in the Pejinsylvania Appalachians west of Har- 

 risburg, where 81 miles were compressed into 66 miles, thus involv- 

 ing a shortening of 15 miles in this much narrower belt.^ The 



^Jour. Geol., XVIII (1910), 235. 



