120 EEPORT UNITED STATES GEOLOGICAL SURVEY. 



dip and strike. These cases, however, may be regarded as the excep- 

 tion rather than the rule. So far as practical work is concerned, there 

 is no donbt that the ore-veins of these regions are inexhaustible ; *, e., 

 they will reach to depths beyond which the miner of the i)reseut day 

 cannot penetrate. Improved machinery for supplying deep mines with 

 cool air and controlling the waters may at some future time permit of 

 still dee])er workings. 



Summit District. — Southwest of Del Norte a number of mines are 

 located in what is called Summit district. The "Little Annie'' first 

 drew attention to the place, and soon other mines were opened. Gold 

 is the metal found there. In 1875 I visited the locality and examined 

 it. So far as could be determined, no regularly-defined veins exist 

 there. The entire hill upon which the ore-bearing rock is found seems 

 to be impregnated with mineral matter. This latter is essentially 

 l)yrite, occurring in very minute crystals or particles. It is highly au- 

 riferous within certain zones, and upon decomposition the gold becomes 

 free. Thus a very satisfactory yield can be obtained by milling the 

 ore. It remains to be established whether the impregnation will con- 

 tinue to be gold-bearing throughout the entire mass. In other regions 

 I have observ^ed similar impregnations of the same mineral, but as no 

 mining was going on there it became impossible to decide as to their 

 merits. Nearly all the mines in Summit district were but in their 

 infancy, and it therefore cannot be stated what their ultimate pros»- 

 pects or probable fate may be. 



San Juan region. — During the year 1874 I had occasion to visit the 

 entire San Juan region while accompanying the party in charge of Mr. 

 A. D. Wilson. At that time not all the'lodesor even their localities 

 had been discovered. Since we were there the districts on Lake Fork, 

 near Handle's Peak, and others have been organized. Ilowardsville 

 and Silverton were the centres of all mining operations. 



Early in 1860 and 1861 the metalliferous character of the locality had 

 been recognized by Baker, and he led into the country a large party of 

 prospectors and miners. Hardships and Indians, however, succeeded 

 in disbanding them, and many perished. Since that time until a few 

 years ago the region was either forgotten or dreaded. In 1873 the treaty 

 with the Utes, ceding the land, was concluded, and miners flocked from 

 everywhere to the spot of which such exaggerated reports had reached 

 them. Many were disappointed and returned with discouraging reports, 

 but more remained and may ultimately reap the reward of their perse- 

 verance. Instead of only Baker's Park, which was the first known, 

 other localities were discovered, and the country was comparatively 

 rapidly settled. 



On the Animas Forks, at Howardsville and at Silverton, the greater i3or- 

 tion of the locations may be found. When I visited the places (August, 

 1874), over 2,000 lodes had been claimed, although but few were steadily 

 worked. Galenite, sphalerite, fahlerz, argentite, and pyrargyrite com- 

 pose the ores chiefly. Silver is almost exclusively the metal obtained, 

 and occurs in large quantities in some of the veins. An exception to 

 this rule occurs in Arrastra Gulch, near Silverton, where the Little Giant 

 mine is worked for gold. Chloride of silver is reported as occurring in 

 some of the Devonian limestones near the Animas Eiver. I did not 

 have time to verify this report. As is the case with by far the majority 

 of ore-veins in Colorado, so these, too, have a dip almost or entirely 

 vertical. This may certainly be regarded the normal for the lodes of 

 the State. Within the last three years lodes have been found and 

 opened in the vicinity of Lake Fork. Besides the usual silver ores, 



