J'olcanic Ash from Lake Su}>erla)'. — Wiiichell <t Grant. 211 
The following table shows the comparative sections found 
along the Rocky Mountain front: 
AGE. MONTANA. 
CANADA. 
COLORADO. 
Eocene. 
Post-Laramie. 
Cretaceous. 
Fort Union. 
Livingston. 
Unconformity. 
Laramie. 
Paskapoo. \ Porcupine hills. 
S,7(X)' '/ WiUow creek. 
(Erosion interval.) 
Edmonton (Tyrrell). 
(Wapiti river, Dawson.) 
\ b. Denver beds. 
> a. Arapahoe beds. 
Unconformity. 
Laramie. 
VOLCANIC ASH FROM THE NORTH SHORE OF 
LAKE SUPERIOR.* 
By N. H. WiNXHELL and U. S. Gkant. 
It is a peculiar feature of that vast series of surface igneous 
rocks, belonging to the copper-bearing series on each side of 
the western half of lake Superior, that deposits of volcanic 
ash are not cominon. In fact, Irving stated that he consid- 
ered such materials as entirely lacking.f Selwyn saw rocks 
on Michipicoten island which he referred to as tuffs;*; and 
this seems to be the only direct reference, made in late years, 
of rocks of this age to volcanic tuffs. In the exandnation of 
a series of rocks belonging to the Geological and Natural 
History Survey of Minnesota, from the north shore of lake 
Superior, several have been found which possess the character- 
istics of fragmental volcanic deposits. The best examples 
of thei?e are Nos. 8A, 17, 24 and 61 of the Minnesota Survey 
collection, § but there are also others which are of the same 
nature but do not show their origin so clearly. The rocks here 
mentioned are from Duluth, or the immediate vicinity, and be- 
long in the series which is usually termed Keweenawan. Some 
of them are probably from the gray sandstone at Duluth 
which Irving said it was barely possible contained volcanic 
ash material.! 
In general these rocks macroseopically resemble finegrained, 
impure sandstones, and they vary in color from reddish brown 
*Presented before Section E of the American .Xssociation for the Ad- 
vancement of Science, August 25, 189G. 
tR. D. Irving: U. S. Geol. Survey, Mon. 5, p. 32, 188.3. 
JA. R. C. Selwyn, Science, vol. 1, pp. 11, 221, 1883. 
§For description of the field relations and localities of these rock 
samples see Geol. and Nat. Hist. Survey of Minn.. 9th .\nn. Rei)t., pp. 
12, 14, 20, 1881. 
II R. I). Irving: Op. cit., p. 138. 
