SUEVEY OF COLOEADO AND NEW MEXICO. 109 



Lastly we emerged upon a precipitous narrow dike of quartz por- 

 pliyry overhanging the before-mentioned creek on its right bank, and 

 forming an abrupt wall of one hundred and fifty feet above its bed. The 

 crystals, both of quartz and feldspar, were very large, averaging the 

 size of a man's hand. The quartz was standing tx^ansparent and milky, 

 while the feldspar was of the true flesh-red color common to typical peg- 

 matolite. 



BOULDEE CITY, JULY 5. 



Obtained specimens of ores from leads ten miles from this place u^) 

 the James Creek. A fine solid specimen of argentiferous galena was 

 given to me from one foot beneath the surface at the intersection of the 

 Buckhorn and Big Thing lodes. Mr. Arnett, the owner of the claim, 

 states that this ore runs from $125 to $200 per ton in silver, and $300 

 in g'old. I also obtained a specimen of very fine-looking ore from the 

 Horsefall mine, ten miles from Boulder City, in Gold Hill. 



Near Boulder City, on the property o^vned by Mr. Marshall, occur some 

 fine exposures of coal, which have been visited by Dr. J. LeConte, and 

 examined subsequently with much care by yourself, so that a special 

 report from me upon them would be superfluous. I will confine myself, 

 therefore, to the mere statement that, in a distance east and west of a 

 couple of miles, there are eleven exi)osures of very excellent coal, at least 

 nine of which would seem to promise rich rewards for the working. The 

 mining which has as yet been done, was merely to fix the location and 

 investigate the extent of the veins, as well as that could be done at the 

 surface. The beds appear to be large enough to yield with proper appli- 

 ances a thousand tons a day for an indefinite time. The commercial 

 value of this coal when the country is a little more settled can hardly be 

 overestimated. The color is a dark brownish or bluish black, with a high 

 luster and low specific gravity. It breaks, as does all of this recent coal 

 which I have observed along the flanks of the Eocky Mountains, with 

 the exception of the rare anthracite, into parallelopipeda. This friabil- 

 ity is annoying to the smelter, who finds that it chokes up his grate bars 

 and stops the draught, but it has been successfully combated in the works 

 of Professor Hill, of Blackhawk, by the use of the staircase furnace. 

 This coal contains very few impurities, and can be and is used in the 

 blacksmith's forge without previous coking. Specimens have been pro- 

 cured from these various veins and will be analyzed at the earliest oppor- 

 tunity and the results submitted to you.* 



GOLDEN CITY. 



Golden City is situated nearly west from Denver, on a gently sloping- 

 plain at the inner extremity of the caiion between two singular mesas or 

 table mountains of igneous rock, capped, like the innumerable mesas fur- 

 ther south, with thick slabs of basalt. The western border of the beau- 

 tiful valley in which Golden City is built, is formed of the gneissic rocks, 

 upon which rest the triassic (partly variegated and partly white) beds, 

 and then follow the Jurassic and cretaceous, but ill-defined on account 

 of the unbroken grassy sward which usually conceals them. The di[) of the 

 tertiary beds is here beyond the vertical, so that they seem to incline 

 toward the mountains. There is a lead of silica in a state of fine divi- 

 sion which has been opened on a hill of triassic. On the west side of 



"*I forward to you as a supplement to this report analyses of some coals from 

 Wyoming Territory, and hope to add the Boulder coals thereto shortly. 



