Geology of (he Lake Superior liecjion. — WincheU. 19 
takable certainties to which he applies distinguishing names. 
This point will be examined more fully later. 
Prof. Pumpelly's attention was given to the copper-bear- 
ing rocks and the sandstones. From his observations made 
on the Penokee and Gogebic ranges, and thence eastward to the 
Ontonagon river, in company with Maj. Brooks, he reached 
the conclusion that the (hipriferous series is conformable 
with the Huronian. A Joint paper by Pumpelly and Brooks* 
expressed the opinion that the Cupriferous maybe more near- 
ly related, in point of time, to the Huronian than to the Silu- 
rian. Like Brooks, he calls the later sandstones Silurian, the 
Cambrian at that time being included in the lower part of 
the Silurian. From this conclusion, however. Brooks later 
recededf and pointed to evidences of the separateness of the 
Keweenawan and the Huronian. 
Dr. Rominger affirms that there is no choice, from strati- 
graphic considerations based on observed facts, but to see in 
the Lake Superior sandstones the equivalent of the Potsdam 
sandstone. "Its lower portions are so intimately connected 
with the sandstones and conglomerate beds of the Copper- 
bearing trappean series that I could draw only an arbitrary 
division line between the two groups, which would swell the 
thickness of the sandstone group to many thousand feet."]; In 
passing through the Portage canal, Keweenaw point, and to 
the west side of the axis of the point. Dr. Rominger made a 
series of careful observations upon the relations existing be- 
tween the eastern sandstone and the western sandstone, and 
thence to the traps. He states that there seemed to be a 
conformable continuation in the descending order, "an unin- 
terrupted serial connection between the trappean copper- 
bearing deposits and the Lake Superior sandstones." (P. ihS,) 
Tliis has never been contradicted as to that locality. 
It appears, therefore, that the result of the Michigan sur- 
vey, touching the relations of these sandstones to each other, 
and of the copper-bearing series to the Huronian, was not 
satisfactorily conclusive. The three principal geologists 
reached dilferent conclusions. It remained for the Wisconsin 
*Am. .Tour. Sci., (8), vol. iii, p, 428. 1872. 
fAm. .lour. Sci.. (3), vol. xi, pp. 206-211, 187(5. 
:t:Michigaii report, vol. i, p. 81 (of roporl on the Paloo/oic rocks), 1873. 
