84 Ore-Deposit of the Treadwell Mine. 
no one who pretends to a scientific education — can afford to 
ignore it. 
NOTES ON THE ORE-DEPOSIT OF THE TREADWELL 
MINE, ALASKA. 
By George M. Dawson, D. S., F. G. S. 
Assistant Director Geological Survey of Canada. Read before the Royal Society of 
Canada, May Sth, 1889. 
The Treadwell mine, situated on Douglas island, Alaska, is 
a somewhat remarkable ore-deposit, and has of late years be- 
come prominent as a producer of gold. I am not aware that 
any systematic description of the character of this deposit has 
yet been published, and this circumstance may render the fol- 
lowing notes on its mode of occurrence of interest, while the 
microscopical examination of the gold-producing rock by Mr. 
F. D. Adams, throws further light on the character of the de- 
posit. My examination of the mine itself was made, by the 
kind permission of Mr. Treadwell, while I was on my way 
back from the Yukon District in the autumn of 1887. 
Attention was first drawn to this deposit, by the discovery 
of gold-placers, which were worked for several years previous 
to the finding of the ore, and in a few cases were found to pay 
well. The gold of the placers was fine, but rough and unworn 
in character. The placers occurred on the surface of the ore- 
mass itself and on the rather steep slopes running down from 
its outcrop to the shore, and must have been produced by the 
natural decay of the ore subsequent to the glacial period, as 
they were found to lie above the boulder-clay, which fills many 
of the hollows and rests directly on the rock wherever it oc- 
curs. It may be noted here in passing, that Mr. Treadwell in- 
formed me that barnacles and various marine shells had been 
found still adhering to the surface of the rock, in places from 
which the clay had been excavated, up to a hight of 150 feet 
above the present sea-level. 
The ore-mass, which has been extensively exposed by strip- 
ping and proved as well by several drifts, has a thickness of 
about 400 feet. Its length, or at least the length of that part 
of it which will pay for working, is not accurately ascertained 
but must be considerable. It runs in a general northwesterly di- 
rection,parallel to the shore of the eastern side of Douglas island 
and is bounded to the northeast and southwest by dark, rather 
slaty argillites, which, from analogy with similar rocks which 
