404 Canadian Record of Science. 
gold in some of the chutes, together with the products of 
alteration, cerussite (Pb Co,), horn silver (Ag Cl), and, 
as accessory minerals, augusite (Pb So,), pyromorphite 
(8 Pb, P, O, + Pb Cl,), minium (Pb, O,), blende( (zn Fe)s), 
colamine (zn § O,), and also native silver. The discovery 
of this new ore-bearing horizon, so unusual and hitherto 
entirely unsuspected, began a new era of vast importance 
to the West and even to the world, as a new territory of 
large extent was found to the prospector and miner, great 
ore beds extremely suitable for smelting all classes of ores 
of the precious metals, owing to the presence of much lead 
that gathers within itself all the gold and silver in the 
molten rock of the furnace and then separates from the 
slag completely, made feasible the present enormous smelt-’ 
ing plants; and the production of silver increased with 
such prodigious strides as to raise the world’s supply, thus 
lowering the ratio value of silver to gold, in as much that 
the price of silver has depreciated from $1.30 to 83 cents 
per ounce. 
The most ancient rocks at Leadville are Archean gran- 
ites and gneisses, the veritable backbone of the Rockies, 
upon whose flanks lie successively, but little uptilted, Cam- 
brian quartzites or Potsdam, Silurian dolomitic white lime- 
stones, Carboniferous limestones (including the “ Blue”), 
grits and shales, and finally rocks and beds of much later 
epochs. Overlying the Lower Carboniferous limestones, 
i. é., the “ Blue,” particularly so at Leadville, or forced in 
along bedding planes, or cutting obliquely the stratification 
in dyke-form, is the all-important igneous rock of different 
varieties of fine-grained quartz diorite or “ porphyry,” as it 
is locally called; all-important in that this intrusive rock 
has undoubtedly played a most important role in perhaps 
being the source of the ore or else a very potent agency in 
its deposition in these sedimentary formations. Faults 
occur, some of considerable throw, along which ore is sel- 
dom found, except fragmental stuff dragged along the fault 
planes from the regular ore bodies, although in some work- 
