318 



GEOLOGY OF THE DENVER BASIN. 



The increase for the years 1867 and 1868 and the subsequent decrease 

 is attributable to temporary activity in metallic mining and milling during 

 those years. 



In the summer of 1870, upon the completion of the Denver Pacific 

 Railroad from Cheyenne to Denver, the Kansas Pacific, and the Colorado 

 Central from Denver to Golden, the demand upon the mines of the foot- 

 hills in Jefferson and Boulder comities largely and permanently increased, 

 their annual production for L870 and 1 ST 1 being respectively 13,500 and 

 15,860 tons. 



In 1S7"_' the completion of the Boulder Valley Railroad from Brighton 

 to Boulder brought into market the product of the mines — already well 

 developed — at Erie and Canfield. In consequence of this accession the 

 coal production for the Denver fields for the seven years 1872-1878 rose to 

 the following figures: 



Coul product of the Denver fields, 1872-1878. 



The rapidly increasing demands of railways, furnaces, mines, mills, 

 towns, and cities in 1879 — the year of great mining excitement at Leadville 

 and Silver Cliff — caused another notable increase in the coal product of 

 Colorado, the output of the 1 >enver Basin at this time amounting to 182,630 

 tons. This constituted the bulk of the increase for the entire State, the 

 mines of southern Colorado being the only others that showed advance, 

 and these rather in the line of development than owing to conditions of 

 trade. From 1879, however, the latter mines largely increased their 

 capacity and output, while the mines of the Denver Basin temporarily fell 



