Notes on a Great Silver Camp. 403 
Astronomer Royal was, on the establishment of the office in 
1675, declared to be “ to apply himself with the most exact 
care and diligence to the rectifiying the tables of the 
motions of the heavens, and the places of the fixed stars, 
in order to find out the so much desired longitude at sea for 
the perfecting of the art of navigation.” 
NOTES ON A GREAT SILVER CAMP. 
By W. A. Cartytr, Ma.E., of McGill University. 
High up on the Mosquito Range in Colorado, 10.000 feet 
above sea level, two parties of intrepid prospectors simul- 
taneously discovered, in 1860, in California Gulch in the 
Arkansas Valley, paying gold-alluvions, and, with charac- 
teristic rapidity, a large town, ‘‘ Oro City,” sprang up as in 
a night close by what was to become the site of Leadville. 
These alluvial deposits, very rich in gold but limited in 
area, were soon exhausted in three or four years, when the 
inhabitants of this “city ” vanished as quickly as they had 
come, for newer and richer diggings, leaving behind a few 
to carry on a little desultory mining in the gravels and also 
along some quartz-veins that had been discovered near by, 
no thought or search being given for any other metal but 
gold, nor any heed taken of the hoary, iron-stained rock 
that stuck in the sluices, until in 1875, when some miners, 
suspecting what others had not, and sending some of this 
rock to Denver for assay, learned its great value in argent- 
iferous lead carbonates, and by the spring of 1877 active 
prospecting had begun everywhere in this region, and 
“from this time on’ the development of rich and product- 
ive mines advanced with astonishing rapidity.” (Phillips’ 
“ Ore-Deposits.”’) 
These carbonates were soon traced to their source, which 
proved to be a dark-colored bluish limestone, which thus 
has ever since been known as the ‘ Blue” limestone, form- 
ing the lowest member of the Carboniferous series, that is 
- quite extensively developed through this part of the West. 
The ore was found to consist of silver-bearing galena, with 
