NOTES ON SOME OXIDISED COPPEE ORES. 473 



5 to 10 dwts. of gold to the ton. These young mines are being 

 worked on a considerable scale, the monthly output of matte 

 from the group being over 300 tons, the product of about 1200 

 tons of ore. This quantity is easily treated in two small water- 

 jacket furnaces — and as there are coal mines near by and coke is 

 cheap, it would seem that the mines are likely to be very profit- 

 able whatever may be the price of copper. 



Situation and physical description of the Torreon Mines. — These 

 mines are situated in the province of Chihuahua, Old Mexico. 

 The Mexican Central Railway, on leaving the valley of the Eio 

 Grrande at El Paso runs for over 500 miles through a succession 

 of plains which are so slightly separated from each other by 

 occasional gentle elevations and depressions as to seem practically 

 one. The surface of the plain, gradually rising from a little over 

 3700 feet above sea level at Paso del Norte (now the city of 

 Juarez) reaches an elevation of 5448 ft. at Grallego, 140 miles to 

 the south, and, after several almost imperceptible undulations 

 falls again at Lerdo in the State of Durango, which is over 500 

 miles south of El Paso. 



The average width of this extended plain is from 10 to 15 

 miles, and it is for the most part bounded by mountains of 

 fantastic form but moderate elevation on both sides. To the 

 traveller by rail or road these mountains seem much smaller and 

 nearer than they really are, owing to the prevailing clearness 

 of the atmosphere. Terrazas station, 25 miles north from 

 Chihuahua is something over 5000 feet above sea level, and here, 

 among the hills on either side of the railway, a new mining 

 district is being gradually opened up, which bids fair to become 

 of considerable importance in the immediate future, both for 

 lead and copper — the ores of both being largely enriched by the 

 presence of notable proportions of silver. 



Stratigraphy. — The surface of the plain is, like that of most 

 other extensive plains, composed of detrital deposits, and the 

 detritus is in most places very deep. In some parts it is merely 

 loose sand and gravel, but mostly it is covered by good " buffalo " 

 and other grasses, and affords sustenance to large herds of cattle. 

 At Terrazas, which is situated midway between two gentle 

 depressions occupied by the rivers Sauz and Sacramento, a well 



