76 TJic Anicncan Geologist. August, i898 
in perpendicular cliffs, as eroded by the St. Croix river, at 
several points in the near vicinity, forming the celebrated 
St. Croix dalles. The demolition of these older rocks by the 
ocean shore wonld fnrnish a coarse bouldery conglomerate 
which at a slightly later date, or at more distant or more shel- 
tered points, wonld be bnried nnder a finer tufaceons or gritty 
stratnm, the prodnct of gentler action. This succession 
seems to have formed the conglomerate and the overlying grit 
here described. 
The significance of this fragmental and tnfaceous member 
in the midst of the otherwise wholly igneous rocks of the 
Keweenaw^an, at Taylor's Falls becomes apparent when it is 
compared with what we know of this formation further north. 
About a year ago, in studying the rocks gathered at Duluth 
bv the geological survey, it was found that a similar grit oc- 
curs there in the midst of the trap rocks, lying upon a large 
series of surface flows and derived from them, at the bottom 
of which is the chief gabbro mass of the region. It was also 
found that two conglomerates succeed each other, in the St. 
Louis valley, one containing eruptive materials and the other 
not. It was also found that the record of the deep well sunk 
for gas! at a few miles west from Duluth demonstrated two 
eruptive series separated by a grit or quartzyte and by other 
fragmental debris. At a later date it has been found that at 
several places on the north shore there is a conglomerate 
and quartzyte at the bottom of the upper portion of the trap 
series. This conglomerate indicates in several places a" pro- 
found non-conformity. It succeeded, in time, the iVnimikie 
formation and the gabbro dikes of Pigeon point, and the apo- 
rh}-oI_\tesor"red rocks" which are associated with the gabbro. 
In short, about Grand Portage this break in the formation, 
separating the Animikie and the gabbro with its surface flows 
from the later traps is most clearly demonstrated. It has be- 
come our custom to designate the gabbro and its eruptive 
age Norian, and the overlying conglomerate and quartzyte, 
with the basic flows which succeeded them, Keweenawan; 
and we have been able to locate this conglomerate at several 
points between Duluth and Grand Portage. Thus it appears 
that in Minnesota, extending from Taylor's Falls to Grand 
Portage bay, the eruptive rocks which it has been customary 
