532 GEOLOGY AXD MINING INDUSTRY OF LEADVILLE. 



London mine. — Tliis is the uiost promising of these elevated deposits, and 

 has been known for a long time; but, besides the natural difficulties of its 

 position, apparent bad management and contested ownership have com- 

 bined to retard its development. Fuel being expensive at such an altitude, 

 the novel idea was adopted of using wind as a motive power, and a powerful 

 and strongly constructed windmill was built near the mine; but it proved 

 incapable of resisting the force of the fierce winter storms which sweep 

 over Mosquito Pass, and was blown down the first winter after its erection. 



The geological horizon of the deposits, as explained in Chapter IV (p. 

 142), is apparently near the junction of the White and Blue Limestones, at 

 the contact with a sheet of White Porphyry lying parallel with the stratifica- 

 tion. It is there shown that the strata are here turned up at a steep angle 

 against the London fault on its west face, and that as their strike makes 

 an acute angle with the plane of the fault, they are gradually cut ofi" by it, 

 successively higher horizons coming in contact with the fault line as one 

 goes across London Mountain from north to south. This is shown in a 

 general way on the map of the Mosquito Range; but it must be borne in 

 mind that the line of fault could not be traced with absolute accuracy, owing 

 to its covering of debi-is, and that, even if it could have been, the scale of the 

 map is too small to repi'esent the necessary details of structure. This is a 

 point of great intei'est as regards both its geological structure and the light 

 its exploration might throw upon the genesis of ore deposits, and it is to be 

 regretted that the underground workings of the mine had not been suffi- 

 ciently extended to aff*ord more definite data on these points. In the single, 

 somewhat hurried visit that could be made only a cursor}^ view could be 

 obtained of the ore deposits and their surroundings. They consist of two 

 so-called veins, parallel and about forty feet apart, standing nearly vertical 

 and striking about northwest and southeast Of these, the southwestern 

 has an average thickness of about four feet and is exti'emely well defined. 

 It carries sulphurets of lead, copper, and iron, with some gold. The north- 

 eastern body is a free-gold ore, impregnating the country rock for about 

 two feet in thickness. Both have been proved in a length and in a height 

 abo^•e the tunnel level of several hundred feet, and the ore was said to 

 average S40 per ton and upwards, consisting in considerable proportion of 

 free-millino: ore. 



