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408 Canadian Record of Science. 
most prosperous mining town in the West, whence during 
the last year ore to the valuc of $10,000,000 was shipped to 
the smelters at Leadville, Pueblo or Denver; and for sey- 
eral years the writer was engaged in engineering work that 
took him into nearly all the great mines, where was 
learned some insight into the intricacies of the geology and 
the character of the ore deposits. 
A vertical section through Aspen Mount transverse to 
the strike would reveal : 
(1) Archeav granites; (2) Cambrian quartzites; (3) 
Silurian dolomitic limestone; (4) Lower Carboniferous 
limestones, 7. e., the “ Blue” and the “ Brown”; (5) Middle 
Carboniferous shales and shaley limestones; (6) intrusive 
diorite; (7) Middle Carboniferous limestone (grey); (7) 
Jura-Triassic sandstones. In this district many differing 
conditions are noted when compared with Leadville. Here 
it is seen that a great part of the originally calcareous 
‘‘ Blue” limestone has been altered to dolomite by mag- 
nesian waters permeating the stratum, and that the whole 
of the lower part, together with narrow bands in the upper 
part or the “ Blue,” has been thus dolomitized,’ and is known 
in the miner’s phraseology as the “ Brown” limestone, from 
the brownish color due to the oxidation of iron along faces, 
These terms “ Blue” and ‘‘ Brown” limestones became both 
common and important, as the belief was almost general for 
some years that the Aspen silver horizon was along the 
bedding plane or “contact ”’ between the limestones, as the 
ore fora long time certainly seemed on first examination 
to be thus located, and hence long and expensive lawsuits 
arose. By the United States mining laws, a claim 1,500 
feet, with parallel end lines 50600 feet long, according to 
local laws, must be located along the outcrops or apex of a 
vein or lode, so that the owners may have the right to fol- 
low and mine the ore down along the vein as far as possible, 
even if the vein on its dip passes without the sice-lines and 
1 Papers on Aspen in “‘ Engineering and Mining Journal,’’ June, 1588, by D. W. 
Brunton, M.B., and ‘‘ Transactions of American Institute of Mining Engineers,” 
vol. xvii, p. 155, by Carl Henrich, M.E. 
