406 Canadian Record of Science. 
of the region were derived from circulating waters, which 
in their passage through the various bodies of eruptive 
rocks took up certain metals in soiution; and, concen- 
trating along bedding-planes by a metamorphic or pseudo- 
morphic action of replacement, deposited these metals as 
sulphides along the contact or upper surface, and to greater 
or less depths below that surface, of beds generally of lime- 
stone or dolomite but sometimes also of silicious rocks.” 
Leadville is still producing vast quantities of ore, and 
will continue to do so for many decades, judging by the 
large bodies now exposed; but much of it, however, is of 
very low grade in silver, but very valuable as a fluxing ore 
by reason of the presence not only of lead but a large per- 
centage of iron. It has been proved that throughout the 
whole thickness of the ‘‘ Blue” limestone ore bodies may 
be found, and that, besides running in chutes through the 
main body, as large and persistent ore bodies are being 
found at the bottom of this limestone along the ‘ grey por- 
phyry,” an intrusion of igneous rock of later date than the 
“white” first met with above, that not only underlies this 
limestone but sends tongues up through even into the older 
porphyry, or intercalates sheets along the. stratification 
planes, significant of the tremendous internal forces that 
can wedge apart with molten rock the strongly bedded 
limestones weighted down with thousands of feet of super- 
imposed strata. 
Very soon prospectors, now aware of the ore bearing 
possibilities of the “Blue” limestone, guided in some de- 
gree by Hayden’s Geological Maps, quickly scattered along 
the ranges, along whose sides the basalt edges of those 
deeply formed formations are now exposed, having been 
forced up by some of the great mountain-forming move- 
ments that have pushed up granite core masses through the 
great overlying thickness of sedimentary rock, crumpling, 
contorting and faulting them, or else re-elevated the veteran 
primal mountains, around which as islands flowed the Car- 
boniferous seas. For geological evidence there seems to be 
that these main ranges of Archzean age that form the: con- 
