RELATION OF GABBRO AND PERIDOLITE. 391 



iious often for many miles, as is evidenced by the frequent long and regular 

 dikes and the quartz veins. 



Gabbro. — In Bagley creek, north of the point where the serpentine dike 

 crosses the creek, there is an exposure of a typical gabbro, containing a good 

 deal of plagioclase (probably labradorite) and fresh diallage. In one crystal 

 a regular narrow band of monochroic rhombic pyroxene extends through a 

 diallage crystal, forming twins, such as are figured diagrammatically by Levy.* 

 This gabbro has associated with it a finer crystalline mass, apparently a part 

 of the same magma, a slide of which shows the rock to be decomposed to an 

 aggregate apparently largely quartz and feldspar, showing one quartz pheno- 

 cryst with corroded borders, some plagioclase with twin lamellae, and a 

 little pyroxene. This finer grained material may be seen just south of the 

 typical gabbro exposure in the bed of the creek. On the northern edge of 

 the gabbro there is a sulphur spring. Here was obtained the series of speci- 

 mens comprising series I of those described in Dr. Melville's supplement. 

 Number 175 is the undecomposed gabbro; numbers 173 and 175 seem cer- 

 tainly merely weathered layers of the gabbro. 



Between this gabbro and the serpentine lies a body of AuGella-hearing 

 shale a few hundred feet thick ; so that it has yet to be demonstrated that 

 there is a genetic connection between the gabbro and the peridotite, a posi- 

 tion which was at first taken and which still seems to me probable. 



Mineral Deposits. 



Precious Metals, etc. — Various metals occur in the mountain. Gold was 

 found by Dr. Melville, associated with chalcopyrite and bornite, in a speci- 

 men of ore from a copper prospect in a ravine draining into Mitchell canon. 

 A considerable amount of work has been done in prospecting for copper in 

 the vicinity of Eagle point. Black point, and Pyramid hill, but no large ore 

 body was ever discovered. The copper ore seems always associated with 

 diabase. 



The so-called silver mine in the northern slope of Pyramid hill (Mount 

 Zion) is said to contain some manganese. Cinnabar has been mined about 

 one mile northeast of North peak. The ore is here directly associated with 

 chromite. In proximity to the ore there is a ledge of the so-called quick- 

 silver rock, largely opal, with some serpentine. In the ravine a little way 

 below the mine there is a sulphur spring. Further down the slope, by the 

 road that runs near the eastern base of the mountain, there is another spring 

 that must have been very active in past times, as it has deposited a large 

 amount of travertine. South of this spring deposit, by a branch of Marsh 

 creek called Ferguson creek, there is a little butte of micaceous andesite. 



*"Mineraux des Roches," 1888, p. 201. 

 LVIII— Boll. Geol. Soc. Am., Vol. 2, 1890. 



