248 R. D. Irving—Divisibility of the Archean. 
latter formation he took as his type the series of rocks which is 
displayed along the north shore of Lake Huron, between the 
t. Mary’s and Thessalon rivers) Having examined this for- 
mation somewhat thoroughly, I have no hesitation. in saying 
that in it we find the equivalent of the iron-bearing slates of 
the Marquette and Penokee regions, in which opinion I merely 
follow a succession of geologists. Like the latter formations it 
is in the main composed of quartzite and slate, with various 
cherty and limestone beds, and with many included eruptives, 
and like them also it is distinctly a feebly altered series. 
Where its basal quartzite member comes into contact with the 
underlying gneiss, which forms the north shore of Lake Huron 
iles east from Thessalon River, and which 
has been mapped by Logan as Laurentian, a most beautiful 
asal conglomerate is to be seen. The quartzite, here little 
more than a feebly indurated sandstone, becomes thickly 
crowded with masses of granite, gneiss and schist, the quartz 
sand of which the rock is usually composed giving place, also, 
in large measure, to an unassorted detritus plainly derived 
from the adjacent gneiss. 
Sir William Logan’s able successor in charge of the Geolog- 
ical Survey of Canada, Dr. A. R. C. Selwyn, has recently said 
that Logan nowhere asserts an unconformity between his Lau- 
rentian and Huronian, and, indeed, that he could not have be- 
lieved in such an unconformity. To me, however, it seems 
a that Dr. Selwyn must be mistaken as to this. That Logan 
elieved in such an unconformity seems evident to me from his 
sections of the region north of Lake Huron in the atlas (Geo- 
logical Sections, Plate I) to the Geology of Canada (1863), 
and in his descriptions given in that volume, although he does 
not make the statement in so many words. In speaking, for 
instance,.of the contact of the Huronian with the gneiss on Lake 
Temiscamang, he describes it as filled with fragments from the 
gneiss. ow, manifestly, such an occurrence, on Logan’s 
plainly expressed view as to the sedimentary origin of gneiss, 
can only be explained by a great time-gap between the two 
formations. 
It is, of course, well enough known to any geologist, who 
has worked with these older formations to any extent, that the 
terms Laurentian and Huronian have been greatly abused, hav- 
ing been applied often on the very feeblest of lithological evi- 
dence t is also manifest to any one with such experience 
that where the two series are infolded, as in the Marquette re- 
