3o6 The American Geologist. ^'ovember, i904. 
such copper Ijcd in the sandstone of Porcupine mountain, far 
from an eruptive outflow." Posepny seems to have heen influ- 
enced in the first place by a strong- prepossession as to the role 
of ascending solutions, and in the second place by the oc- 
currence of the ore as a mineral or rarely sulfide and not as 
carbonate. 
Prof. \'an Hise in his very interesting article on "Some 
Principles Controlling the Deposition of Ores/' uses the metal- 
lic copper deposits as a conspicuous illustration of ore deposits 
where the concentration by ascending waters has been suffi- 
cient without secondary concentration by descending waters, 
writing as follows : 
"In some cases the deposits thus produced are sufficiently 
rich, so that they are of economic importance. In these cases, 
which undoubtedly exist, but which perhaps are less numer- 
ous than one might at first think, a concentration of ascending 
waters has been sufficient. 
"A conspicuous illustration of ore deposits of this class 
which may be mentioned are the metallic copper deposits of 
the lake Superior region. The copper was in all probability 
reduced and precipitated directly as metallic copper from up- 
ward moving cupriferous solutions. The reducing agents 
were the ferrous compounds in the solid form, in part as 
magnetite and as solutions derived from the iron bearing 
silicate. When the copper was precipitated, the iron was 
changed into the ferric condition. It is well known that me- 
tallic copper once formed is but slowly affected by the oxidizing 
action. Oxidation has, in fact, occurred in the lake Superior 
region, but from the facts now to be observed, not to an ii>i- 
portant extent. An oxidized belt may have formed in pre- 
Glacial times, but if so. it Avas swept away by glacial erosion, 
and sufficient time has not }et elapsed to form another. The ore 
deposits now worked have apparently remained practically un- 
changed since the time of their concentration. In this fact we 
have the explanation of the great richness of these deposits to 
extraordinary depths." 
Prof. H. L. Smyth, of Plarvard. has also adopted the 
same belief and I have already discussed it in Vol. VI. of our 
reports. Prof. Smyth believes that the various flows were 
surface weathered and the earlier non-alkaline minerals pro- 
