124 GEOLOGY AND MINING INDUSTRY OF LEA.DVILLE. 



granite, through which 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 fifty feet wide runs across the basin in an easterly 

 direction from the base of Democrat 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 fine, 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 lake. 



In this raised basin many eruptive dikes, mainly of porphyrite, 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 hornblende 

 and mica. They occur frequently in the form of interrupted dikes. That 

 found near the uppermost of the lakes contains both hornblende 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 fluidal 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 

 variety of the Leadville rock; fragments of the same rock are abundant in 

 the dtibris 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- 

 ernwall of the latter. A double dike of similar appearance occurs further- 

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



