298 GEOLOGICAL SURVEY OF THE TERRITORIES. 



wall could be observed. Clay selvages at some places border the ore- 

 vein, but the rock on the outside may contain numerous spurs of that 

 same vein. It is altogether one of the most interesting mines. I did 

 not succeed in discovering any distinctly differing gangue-rock; it 

 appeared throughout to be the porphyritic granite that filled the places 

 between the single veins and spurs. At certain points, circumstances 

 had favored decomposition, and the gangue, therefore, was soft enough 

 to break with the fingers. Quartz and feldspar were its main constitu- 

 ents: but the black mica, characteristic to the surrounding granite, was " 

 just as plentiful as in the gangue itself, so that the conclusion presented 

 itself that, although this gangue must be regarded as younger than the 

 surrounding rock inasmuch as it is decomposed, its ingredients were 

 formed contemporaneously with those of the granite. From 3 to 20 

 inches in the thickness the main vein varies, sending offshoots and spurs 

 to either side ; sometimes they return again, sometimes they pinch out. 

 In several instances, a .number of smaller veins were observed to run 

 parallel to each other, continuing so for a considerable distance. This 

 was the case at the extreme north and of one of the lower levels, and 

 at this point our section of the lode was taken. (Plate YI.) Granite 

 forms the gangue-rock, somewhat decomposed in the central portion, 

 perfectly sound and hard outside, containing within it four distinct 

 parallel veins, the largest one 5 inches thick. Toward the southeast 

 the veins seem to become more irregular. 



Galeuite forms the greater portion of the ore ; associated with it are spha- 

 lerite, pyrite, (rare,) argentite, fahlerz, and pyrargyrite. 



A larger number of mineral species occur in this mine than in any 

 other I have had occasion to visit in Colorado. Galenite is found in 

 almost every variety ; very pretty crystals (combination of cube with 

 octahedron, the latter predominating) of it occurring ito small cavities 

 near the veins; sphalerite, pyrite, and chalcopyrite, massive; pyrar- 

 gyrite, in minute crystals ; argentite, stephanite, polybasite, in tabular 

 crystals; stibnite, rare; silver in form of wire, and leaf-silver; flu- 

 orite, in ligbt-green transparent cubes ; baryte, orthoclase, oligoclase, 

 caolinite, biotite, and quartz occurring between the single veins. 



As stated above, a tunnel of 340 feet leads at a right angle to the 

 vein ; thence levels are driven on either side, and a shaft sunk. The 

 mine is renowned for its rich ore, which, as I was informed, is some- 

 times regarded by strangers as a favorite souvenir of Georgetown. Be- 

 sides the lodes spoken of, a very large number have been claimed, and 

 are worked to some extent. Several of the larger ones were not in op- 

 eration during my stay at Georgetown ; others were in litigation, so that 

 no data regarding them could be obtained. 



The Pay rock mine, situated on Republican Hill, northwest of George- 

 town, I will now mention. Striking nearly due east, the vein pitches 

 downward from the north at an angle of about 20° below the horizontal, 

 and suddenly takes a turn of 45°, (Fig. 2,) so that its dip southward is 

 only 25° instead of 70"^. Porphyritic granite forms the foot- wall, gneiss 

 the hanging^ although at several points they seem to shade . into each 

 other. 



About nine miles west of Georgetown, McCiellan Mountain is located, 

 immediately opposite Gray's and Torrey's Peaks. On the western slope 

 of this mountain, the Baker and other mines are located ; on the east- 

 ern, the International and Belmont. The International strikes about 

 north 30° west, and is a contact-vein between gneiss on the north and 

 granite on the south side. Its location, about 500 feet above timber- 

 line, causes the ore to be frozen almost constantly; while, on the other 



