124 GEOLOGY AND MINING INDUSTRY OF LEA.DVILLE. 



granite, through whicli run irregular vein-like masses of white pegmatite. 

 The latter are particularly prominent on the northeastern walls of Buck- 

 skin canon, a short distance above the town of Buckskin Joe. In the bottom 

 of the upper part of the basin is a small lake, above which a dike of horn- 

 blende diorite forty to tifty feet wide runs across the basin in an easteily 

 direction from the base of Demociat Mountain and disappears under the 

 debris slopes on the other side. 



At the south base of Democrat Mountain are three small lakes or tarns, 

 on a raised shoulder or knoll of granite, back of which is a small raised basin 

 extending to the base of the mountain. This granite is of the tine, even- 

 grained type without large porphyritic crystals, almost white in color, 

 and contains both biotite and muscovite. It is traversed by many small 

 veins of pegmatite, consisting of orthoclase and quartz and often having 

 a regular banded structure, like that shown in Fig. 2, Plate IV, which is from 

 a sketch of a bowlder standing near the lakt^ 



In this raised basin many eruptive dikes, mainly of porplivrite, were 

 observed, only a few of which it has been possible to delineate on the map. 

 These porphyrites belong to the types carrying either mica or iiornblende 

 and mira. They occur freipiently in the form of interrnpted dikes. That 

 found near the uppermost of the lakes contains both honililende and mica, 

 with considerable quartz, and is remarkable for the numerous fragments of 

 Archean rocks included in it. One of these fragments was several feet 

 square and penetrated in all directions by veins of porphyrite, in which a 

 distinctly iluidal structure of the elements of the porphyrite about it could 

 be observed. 



Near the middle lake is a dike of White Porphyry, a fresh and compact 

 variet)- of the Leadville rock; fragments of the same rock are abundant in 

 the debris pile at the head of the gulch. 



One of the porphyrite dikes, which dips 30° to 40° north, can be traced 

 to the south shoulder of Democrat Mountain, which forms the divide 

 between this and the Platte amphitheater, and apparently connects with the 

 long dike, which can be traced as a thin black line high up along the east- 

 ern wall of the latter. A double dike of similar appearance occurs further 

 south on the same divide, near the north base of Mount Buckskin. 



