OF DENISON UNIVERSITY. 
141 
The schists have been fully described. There are constantly metamor- 
phosed at contact with the granite and are perforated by dykes of di- 
orite and felsite in the stratification, the former being derived from the 
fused lower part of the schists, the latter from the upper part of the 
granite more or less modified by contact with the schist. The schists 
and schist-conglomerate especially have in several places been altered 
to porphyry and felsite-porphyry by contact with the eruptives with or 
without obliteration of the schistose structure. 
The third group consists of basement conglomerates consisting of 
fragments of all the varieties of rock included above, which it is possi- 
ble to trace to their immediate source in the high cliffs adjacent. Pe- 
riodic overflows of igneous matter have left vast sheets of diabase, 
diabase-porphyrite, and diabase-aphanite, varying into so-called ash- 
bed diabase, distributed irregularly with amygdaloids and pseud-amyg- 
daloids in great variety. These flows were often apparently sub-aquatic 
and the strong interaction between the sedimentary and eruptive in 
presence of superheated steam or slowly percolating water has caused 
the concentration of metals along contact zones of the amygdaloids. 
The great quantity and area of the overflows caused extensive fusion 
in the conglomerates in places, possibly producing a part of the quartz- 
porpyry and porphyritic conglomerates. The large quantities of cal- 
cite in this whole series is taken as proof of its essentially metamor- 
phic character (in the sense of local derivation from existing materials.) 
There is no evidence in this region that there were extensive eruptions 
of acid rocks to furnish the materials for the clastic members, all the 
conglomerates being easily derived from the adjacent cliffs of granites 
and schists. No gabbro or allied rock which could be identified as an 
eruptive of Keweenaw age was seen. It is evident that a very con- 
siderable interval must have elapsed since the disturbance of the schist 
prior to the formation of the Keweenaw conglomerates lapping upon 
them. Erosion of enormous extent must have gone on and the mate- 
rials may have been transported far into what is now the bed of lake 
Superior. If this be the case, of course the base of the Keweenaw is 
not exposed at all, but is situated far southward and the marginal part 
very likely displays very different characters from that nearer the axis 
of depression. 
We desire, finally, to acknowledge the kindness of the Hon. Rob- 
ert Bell, the distinguished geologist of the Canadian Geological Sur- 
vey, for literary aids, and to disclaim any hope to do more in this pa- 
