202 KEMPS ORE DEPOSITS. 



90 feet square, lying off the north shore of Lake Superior just out- 

 side of Thunder Bay, and within the Canadian boundaries. The 

 native silver was detected outcropping beneath the water. The 

 vein was productive to a depth of 800 or 1000 feet, but below this 

 it yielded little. The trap dike has usually been called diorite, 

 but is determined to be norite by Wads worth (Bull. 2, Minn. 

 Geol. Survey, p. 92), and gabbro by Irving (Monograph V., U. 

 S. Geol. Survey, p. 378). Some $3,000,000 was obtained from 

 the mine, yet the expenses were so great in keeping up the surface 

 works against winter gales and ice that but little profit was 

 realized. The vein has been traced 9000 feet but is nowhere else 

 productive. Considerable graphite has been found in the work- 

 ings, and some curious pockets of gas. 1 



2.09.06. Example 42. Thunder Bay, Canada. The mainland 

 near Silver Islet contains many similar veins. They have fur- 

 nished considerable silver as argentite in a gangue of quartz, barite, 

 calcite, and- fluorite, and associated with zincblende, galena, and 

 pyrite. 2 



THE REGION OF THE ROCKY MOUNTAINS AND BLACK HILLS. 



NEW MEXICO. 



2.09.07. Geology. The general topography and geology of 

 New Mexico were outlined in the introduction. Much remains to 

 be done in developing its geology. The eastern part belongs to 

 the prairie region and is very dry. A few rivers, notably the 

 Pecos and the Rio Grande, afford water for irrigation, the former 

 of which is now being utilized on a grand scale, and for the latter 

 plans have been prepared. In the central portion many subordi- 



1 R. Bell, Engineering and Mining Journal, Jan. 8 and 15, 1887. See 

 also May 14, 1887. W. M. Courtis, '" On Silver Islet," Engineering and 

 Mining Journal, Dec. 21, 1873, and M. E., V. 474. E. D. Ingall, Ann. Rep. 

 Can. Geol. Survey, 1887-88, Part II., p. 14. F.A.Lowe, "The S.lver 

 Islet Mine and its Present Development," Engineering and Mining Jour- 

 nal, Dec. 16, 1882, p. 321. T. MacFarlane, "Silver Islet," M. E., VIII. 226. 

 Geol. of Canada, 1863, 717. Canadian Naturalist, Vol. IV. , p. 37. McDer- 

 mott, Engineering and Mining Journal, Vol. XXIII., Nos. 4 and 5. 



2 R. Bell, "Silver Mines of Thunder Bay," Engineering and Mining 

 Journal, Jan. 8 and 15, 1887. E. D. Ingall, Ann. Rep. Can. Survey, 1887- 

 88, Part II., p. 1H. Rec. See also Engineering and Mining Journal, 

 May 14, 1887 ; Feb. 18, 1888, p. 123 ; May 26, 1888, p. 383. 



