20 GEOLOGY OF THE DENVEE BASIN. 



overlapping those previously deposited. Ilenee, at the present day, this 

 formation is found to be thickest along the southern portion of the foothills 

 and to reach its greatest attenuation at Golden. 



The neighborhood of Golden has been the scene of a peculiar series 

 of deformations in this and succeeding periods which merit especial mention. 

 From the minute study made by Mr. Eldridge of the existing beds and 

 the character and position of their outcrops, it appears that already at the 

 close of the Carboniferous movement there must have been a ridge or arch 

 of Arcliean locks about 4 miles wide extending out eastward at right angles 

 to the general shore-line, which was above water during the early part of 

 the Wyoming period and became subject to sedimentation by sinking below 

 the ocean-level only toward the close of the period. It is not possible now 

 to sav what was the cause of the arching up of the sea-bottom at this point, 

 whether it was due entirely to a movement within the rocks or in part to an 

 unequal planing down of their surface by erosion. That there was a defor- 

 mation of the crust, however, is rendered probable by the fact that in later 

 movements there must have been a repetition of the arching which raised 

 this portion of the surface successively above the general level of the sea- 

 bottom and thus prevented sedimentation for a time at this locality. It is 

 the proof of the repetition of this movement which forms the most convinc- 

 ing argument against the hypothesis of an overthrust fault at this point, 

 which would be suggested by a first glance at the present disposition of the 

 outcrops of the successive strata as represented on the geological map. 



The strain which produced this local arching may be assumed to be a 

 compressive force acting in directions parallel with the shore-line, as con- 

 trasted with that which produced the final general upturning of the beds, 

 which must have acted at right angles to this direction. 



UPPER WYOMING FORMATION. 



The beds assigned to this division by Mr. Eldridge consist of about 

 185 feet of red sandstones and shales, with some thin limestone bands, 

 followed by 300 to 400 feet of shales, variegated in color and gypsiferous 

 in the upper part and ending- in a persistent band of pink and brown 

 sandstone. 



