234 KEMP'S ORE DEPOSITS. 



classification of our volcanic (effusive) rocks rests largely on Von 

 Richthofen's early studies, and that perhaps the most important 

 generalization of late years is due to the work of Hague and Id- 

 dings on the same. Von Richthofen (1885) described the ore body 

 as filling a fissure on the contact of a so-called syenite and an 

 eruptive rock that he called "propylite." The ore and gangue 

 are thought to have been brought up from below by.solfataric ac- 

 tion, in which fluorine, chlorine, and sulphur were the principal 

 dissolving agents. Clarence King (1867-68, published in 1870) 

 brings out forcibly the fact that the footwall of the vein approxi- 

 mates closely the natural continuation of Mount Davidson, and 

 contends that the vein filled a fissure between the syenite of which 

 Mount Davidson consists and the late Tertiary eruptive rocks 

 poured out against its flanks. He traced the geological succession 

 of these and explained the filling of the vein by solfataric action, 

 attendant on a thin dike of andesite, which forced its way into the 

 contact. J. A. Church (1877) thought that the diorite (called sy- 

 enite above) of Mount Davidson had been poured out originally in 

 thin horizontal sheets, w^hich were folded in east and west folds. 

 This was to account for the bedding of the rocks of the lode as 

 now seen. On the diorite was poured out next the propylite, 

 likewise in successive horizontal sheets. Then they were all 

 tilted along north and south axes, and eruptions of andesite pene- 

 trated between their sheets in very large amount. Further move- 

 ments forced the convexities of the first-formed folds against the 

 andesites and crowded their substance sidewise, to some extent, 

 into the synclinals. This movement slightly parted the beds, af- 

 fording watercourses through which rose siliceous waters. These 

 dissolved away the neighboring beds, leaving extensive quartz 

 bodies in their places. They also removed the andesite caps. No 

 ore was formed as yet. Now followed great trachyte eruptions 

 on the east, and they loaded the hanging wall of the lode so 

 heavily as to cause a downward movement of it on the foot, 

 making a new series of openings, and into these poured the ore- 

 bearing solutions which brought the precious metals. No one 

 who has intelligently followed this explanation will doubt that 

 Mr. Church has shown great ingenuity, and yet few would be in- 

 clined to have very much confidence in this long, unnatural hy- 

 pothesis when a simple course will lead to the same results. At 

 the time of Mr. Church's visit the workings were becoming very 

 deep and the great heat which has been since such an obstacle was 



