384 Correspondence. 
the iron ore confounded them in one consideration, and covered them 
both by the same hypothesis, are incorrect. 
Prof. Van Hise is very unfortunate in referring to the general sec- 
tions made of the lake Superior basin by Prof. Irving and published in 
Copper-hearing rocks of lake Superior. Not only is there no evidence in 
the sections themselves that Prof. Irving recognized the unconformity 
which the article he criticises refers to, but, taken with the text, and 
in connection with the diagram on p. 417 of the same work, they con- 
firm unquestionably the statements made by us in the November 
Geologist. In the first place the sections represent "gneiss, granite, 
etc.," as lying unconformably below the Animike, not "gneiss and 
schists," and throughout the volume he describes these as a part of 
the Laurentian. There is at no place in the volume, so far as we can 
ascertain, any reference to the great Keewatin formation — the green 
schists that enclose the Vermilion lake iron ores — which we state are 
also unconformable beneath the Animike. In the next place if we 
examine the diagram given by Prof. Irving on p. 417 of the same vol- 
ume we see at once that the unconformity of which we speak was 
wholly unknown to Prof. Irving at that time, for this diagram repre- 
sents the Huronian "unfolded" as continuous northward and becom- 
ing the "Folded Huronian," and involved there with crumpled Lau- 
rentian in some such way as to constitute what has been separated 
from the Huronian under the name Keewatin. At the foot of the 
same page Prof. Irving shows that he had not apprehended the 
distinctness of these schists from the Huronian, by the following 
statement: "The connection of these folded beds with the unfolded 
is a structural problem still needing investigation." 
Prof. Van Plise is almost equally unfortunate in referring to the 
paper of Prof. Irving in the Am. Jour. Sci. vol. xxxiv, p. 261 ; for the 
schists that Prof. Irving there refers to are not admitted by him, (nor 
either are tliey by Prof. Van Hise) to be iron-bearing, and continuous 
to Vermilion lake. It is true that the non-conformity that is repre- 
sented by Prof. Irving at Gunflint lake,- between the Animike and the 
lower schists and granites, actually does exist. It is also true that the 
same overlap of the Animike is to be seen on later schists, at points 
further west in the direction of the strike of the lower schists, and that 
these slightly higher schists embrace the ores at Vermilion lake. This 
unconformity at these western points, and its identity with that at 
Gunflint lake, was not admitted by Irving— nor is it yet by Van Hise — 
and therein is the complication and confusion that lias arisen in at- 
tempting to apply the same theory for the origin of the iron ores to both 
formations, as represented in the article which is criticised by Prof. 
Van Hise. This lower horizon of schists has been traced carefully and 
'^ This unconformity was described briefly in the same number of 
the Am. Jour. Sci. by A. AVinchell, of the Minnesota Survey. It had 
been first noted by N. H. Winchell in 1878. See the ninth report of 
the Minnesota survey, pp. 10 and 82; also compare Bulletin No. l,of 
the Minnesota survey, p. 33; and the seventeenth report, p. 15. 
