LONDON HILL. ] 43 



very top, of the White Limestone. On the hill above, it can be seen that the 

 fault line crosses the ends of the upturned strata at a very acute angle. 



The point where the easterlj^-dipping Weber Grits beds change their 

 inclination to a sharp western dip, as they must to allow of the coming up of 

 the underlying Blue and White Limestones, as shown in Section C, is not 

 very sharply defined. Some beds of Blue Limestone can be distinguished 

 between them and the fault line, but, while there was not time for exact 

 measurements, and these could hardly have been made without a map, which 

 was entirely wanting at the time of field work, it seems most probable that 

 these upturned beds have been actually compressed against the fault plane 

 to a smaller thickness than they have in a more horizontal position. 



The southwest slopes of London Hill contained no mine openings, and 

 were too much covered by soil and debris to .show clearly defined structure 

 lines, though the sandstone beds of the Weber Grits formation were seen 

 to change their dip from 20'^ to 50°. At the point where the old wagon road 

 descends into the deeper valley of the south fork of the Mosquito gulch the 

 actual fault line can be distinguished, a tunnel having been run in the decom- 

 posed and highly metamorphosed slates and quartzites, which here directl}^ 

 adjoin the granite beyond the fault. This point of contact bears only 10° 

 W. of N. from the dark crag on Pennsylvania Hill, which is nearly on the 

 line of the fault. It is evident, therefore, that there is a sharp bend in the 

 direction of the fault at this point, eveii more marked, perhaps, than that 

 which is indicated on the map, though, as the position of the tunnel has not 

 been determined instrumentally, nor the old road located on the map, it is 

 not possible to fix absolutely the position of this bend. Here for some 

 distance to the west of the fault line the strata stand not only vertically, 

 but have an inclination of 50° to the west; the strike,however, is approxi- 

 mately the same as elsewhere, viz, about N. 20° W. Thicknesses f>f about 

 two hundred feet of vertical strata are exposed, so much altered that their 

 lithological character can with difficulty be distinguished. They include 

 shales and some silicious beds, with one bed of limestone. A short distance 

 to the west of the fault the characteristic sandstones of the Weber Grits 

 are met, with the regular dip of 20° to the northeast. It seems evident 

 that the structure here is the same as that just described at the London 



