246 ROLLIN T. CHAMBERLIN 



old lines of yielding during the critical interval between the folding 

 of the mountains and the establishment of the peneplain, and any 

 such vertical movement whose occurrence and extent have not been 

 detected and duly covered by a correction, would reduce the accur- 

 acy of the calculated results. But on the other hand, any uplifts 

 subsequent to the development of the peneplain do not in any way 

 enter into the problem, for the adopted method of treatment elimi- 

 nates their influence. The testimony of folded mountain ranges in 

 general is to the effect that later episodes of yielding commonly 

 follow along the lines of earlier folding, doubtless because they have 

 become the lines of least resistance. These later episodes of diastro- 

 phism may obviously be either further folding under compressive 

 stress or uplifts with but little folding. The effect of the latter 

 possibility in the case under discussion would be to increase the 

 height of the folded section, without correspondingly adding to 

 the measured shortening, and thus make the calculated depths of 

 the Gore Range block and Front Range block too great. The other 

 alternative of further folding along the old lines is less serious, for, 

 as has been stated before, the outcome of the computations will be 

 the same whether the folding all took place at one time or at differ- 

 ent times, provided the same thickness of shell was affected each 

 time. If two or more episodes of folding deformed different thick- 

 nesses 6i shell, the computed depth resulting from the adopted 

 method of treatment would be in the nature of an average. In this 

 connection it is of significance to note the statement of Hills that 

 the post-Bridger folding was essentially a continuation of the post- 

 Laramie folding, for the second movement began where the first 

 terminated, and if the post-Laramie movement had been further con- 

 tinued the resulting structure might ultimately have been the same.^ 

 In contrast to uplifting, any subsidence of intermontane basins 

 of deposition, or local downwarping, during the critical interval 

 between the mountain folding and the development of the pene- 

 plain would tend to offset the bulging effect of the folding process, 

 and thus lead to a too low estimate of the height of the folded 

 tract. This in turn would result in giving an underestimate of 



' R. C. Hills, "Orographic and Structural Features of Rocky Mountain Geology," 

 Proc. Colo. Sci. Soc, III (1888-90), 419. 



