THE REGION ABOUT GOLDEN. 97 



water. The exceptions noted — the sandy zone midway the Pierre and 

 the more arenaceous beds of the Fox Hills — are, however, not confined to 

 the area under consideration, and therefore bear no relation to tin- phe- 

 nomena here discussed. 



With the general movement at the close of the Laramie and that 

 which produced the unconformity between the Arapahoe and Denver 

 formations along the range, the peculiar structural features here described 

 have nothing to do. 



Fifth period. — Upon comparing Profile IV, PI. X, with the present surface 

 section of the same beds upon the general map of the region (PI. X), the 

 early relations between the arched and horizontal strata, as shown in the 

 profile, are observed in later times to have completely interchanged. 

 The once highly arched strata below the line of unconformity have now 

 assumed a practically direct trend, while the strata above the line of 

 unconformity, originally horizontal, have at the present time a well- 

 defined inward sweep toward the mountains, reaching their limit of devia- 

 tion in the vicinity of Golden, or, the latter feature being considered with 

 reference to the profile itself, the Laramie and overlying strata have 

 acquired a downward bend at the center of the area, directly over the 

 crown of the arch of post-Niobrara times. Compare also figs. 4 and .">, 

 following. 



The final movement which produced the present structural conditions, 

 and the outpouring of the lavas of Table Mountain midway the period of 

 the Denver formation, is regarded as constituting the fifth and closing 

 stage in the geological development of the area under discussion. 



DISCUSSION OF MOVEMENTS PRODUCING THE PRESEN1 sn.'t c TIKI . 

 Statement of the hypothesis upon which the argument rests. Fl'Olll tile Hot infrequent 



occurrence, either within the present area or in other parts of the Rocky 

 Mountains, of compound folds of the S type and of otherwise contorted 

 strata, from the presence of reversed faults, and from the occurrence of 

 the well-known folds en echelon, it is believed that the theory of lateral 

 compression as the means by which the forces uplifting the range were 

 generated, although not accepted l>v all scientists, does, nevertheless, more 

 completely and satisfactorily fall in with the observed facts than any other 



MON XXVII 7 



