286 GEOLOGY AND MINING INDUSTRY OF LEADVILLE. 



the crest of the corresponding anticline on the east side still caps Weston's 

 Peak. It is in the London fault, however, that the relations of the fold and 

 the fault are most clearly seen, because the sedimentary beds still remain on 

 either side to show the structure lines and erosion has cut down into the 

 rock mass so deeply as to afford to the observer actual sections of the earth's 

 crust several miles in length and one to two thousand feet in thickness. 

 These have been described in detail on pages 143-165 and illustrated by 

 sketches in Plates XV, XVI, and XVII, so that it will be hardly worth 

 while to redescribe all the conditions here. 



It is probable that the steepness of the angle of dip of the beds on 

 either side of the fault plane in these cases may be due to a continu- 

 ation of the movement of contraction, or the lateral thrust, since the original 

 faulting and folding, for it is now generally conceded by geologists that the 

 elevation of mountains is continued in a somewhat modified form long after 

 the original dynamic movement, and may very probably be going on at the 

 present day. In the case of the fold at Weston's pass a lateral movement 

 along the fault plane seems also necessary to explain the observed condi- 

 tions. 



This dipping downward of the beds on either side of the fault would 

 seem at first sight to be an exception to what is given in text-books as 

 the rule for the plication of beds adjoining a fault plane, namely, that they 

 bend in opposite directions down toward the fault on one side and up 

 toward it on the other. It is not really so, however, as mature reflection 

 will show. In the case presented by the text-books of strata dipping in 

 opposite directions on either side of the fault, if the beds were brought back 

 to the position they occupied before the displacement, they would be 

 found to have a simple monoclinal fold, such as is described as common in 

 the Colorado Plateau region by the geologists who have written upon it, 

 and which, according to them, is often associated with a fault. These folds 

 and faults differ from those in the greater intensity of the plication and in the 

 different position of the fault plane in regard to the flexure. If one of the 

 S-folds described here could be drawn back to its incipient state of flexure 

 and the strata adjoining it brought to an approximately horizontal position, 

 it would gradually become the monoclinal flexure described by them; or 



