160 The Am eri (•((->} Geohifjliit. Septombor, 1895 
cletennine tlie strutigraphic place of such a transgressive con- 
glomerate, an inspection of the pebbles would decide. If any 
of them consist of the peculiar taconyte, the conglomerate 
must be later than the Penokee series. 
Prof. Van Hise has kindly submitted for examination three 
specimens taken from this conglomerate, viz., Nos. 1)418, 9420 
and 9449 (mentioned on pp. 167 and 169, Mon. XIX, U. S. 
Geol. Survey). They are from sees. 14 and 15, of T. 47-45 W., 
Michigan. The first two of these show no evident taconyte 
pebbles but numerous angular and sub-angular pieces of 
cherty silica, in a dark gray or greenish matrix. No. 9449 is 
similarly composed, but coarser and lighter colored. There is 
near the center of this specimen a large light-gray, impure, 
cherty mass or fragment whose texture and composition are 
not unlike some parts of the taconyte seen in the Mesabi rocks 
of Minnesota, but there are no certain or characteristic glob- 
ular spots in any of the pebbles marking the conglomerate as 
post-Penokee. The conglomerate at the Pahns mine likewise 
shows, in one specimen belonging to the Minnesota survey, 
nothing but debris from the Archean. 
On the north shore of lake Superior this conglomerate leaves 
the Minnesota shore at Grand Portage island. It reappears 
at the west end of Isle Koyale, where it has a large exposure, 
and is overlain by I'ed sandstone.* It is largely exposed north- 
ward from Siskiwitbay. having a strong dip toward the south. 
The northern rim of this island is composed of a dike or series 
of dikes of the type of the Grand Portage and Pigeon Point 
dikes. The shore is high and precipitous and the water very 
deep, caused by the perpendicularity of an immense Animikie 
dike. The overlying Keweenawan conglomerate consists of 
felsitic material of Animikie source, also of some of the hard- 
ened grits of the Wauswaugoning quartzyte. Thus Isle Roy- 
ale is divisible between the Animikie and the Keweenawan, 
the larger portion of it belonging to the latter. The strike of 
these Keweenawan beds is such that they cannot reach the 
Lake Superior shore again until many miles east of Thunder 
bay and Nipigon. In addition to this, they differ so remark- 
ably from the fragmental strata, which at Thunder l)ay and 
Black bay have been considered the base of the Keweenawan 
*Tenth Minnesota report, p. 48. 
