ECONOMIC GEOLOGY OF THE SILVERTON QUAD 
RANGLE, COLORADO. 
I)V P. L. Ransome. 
PARTI. GENERAL DESCRIPTION AND DISCUSSION OF THE ORE DEPOSITS. 
INTRODUCTION AND ACKNOWLEDGMENTS. 
The field work upon which this report is based occupied the season 
of 1890 from the beginning of July to the middle of October. During 
mat summer nearly all of the area was examined and most of the 
nines and prospects were visited. 
The work was resumed in the autumn of L900, with Mr. Alfred M. 
[Rock as assistant, a period of six weeks in August, September, and 
)ctober being devoted to those portions of the quadrangle that had 
iiot been thoroughly studied in the preceding year and to an investi- 
gation of such mining developments as had been effected during the 
vinter. 
It was at one time hoped thai the report of Mr. Whitman Cross, of 
his Survey, on the general geology of the Silverton quadrangle, form- 
ng the Silverton folio of the Geologic Atlas of the United States, 
night be published in advance of this investigation of the economic 
©sources of the district, but owing to various causes his field work is 
lot yet finished. I am therefore unable to use or to cite his results 
n their entirety, or to reproduce his geological map as an adjunct to 
his report. This is to be regretted, as both a thoroughly satisfactory 
reatment and a proper understanding of the ore deposits require a 
nowledge of the geological relationships of the rocks in which they 
ie. This want has been partly supplied by a brief preliminary 
ketch of the geology, kindly furnished by Mr. ( ross. This is neces- 
arily an imperfect outline, to be later replaced by his final results. 
'o Mr. Cross I owe, also, the privilege of publishing a preliminary 
eological map (Pis. IV, V ) of a portion of the area. This map is based 
; pon field work done by himself and his assistants. The geological 
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