NIPIGON LAKE ROCKS—MICHIPICOTEN. 341 
These limestones are of interest, since no such rocks are anywhere else 
known throughout the entire extent of the Keweenaw Series. 
Bell’s statements, thus quoted, certainly seem to show that the Nipigon 
Lake rocks are Keweenawan, and that, to judge from lithological char- 
acters, they belong always low down in the series. I have already stated 
my disbelief in the existence of any one “crowning overflow” closing the 
entire series of Keweenawan eruptions in the. Thunder Bay region. Still 
more doubtful to me seems the reference to this ‘crowning overflow” of 
much of the trap of the Nipigon region. The structural relations of the 
Nipigon Basin to that of Lake Superior would be an interesting subject 
for discussion, but while the structure in the Nipigon Basin itself is so little 
known, speculation on the relations would hardly be profitable. 
SEcTION III.—MICHIPICOTEN ISLAND AND THE EAST COAST OF LAKE 
SUPERIOR. 
Beyond the easternmost of the Battle Islands the north and east coasts 
of Lake Superior, for nearly 200 miles, are composed wholly of rocks more 
ancient than the Keweenaw Series. As shown subsequently, there are 
reasons for believing the Keweenawan rocks continuous in this distance 
underneath the waters of Lake Superior. They first reappear to view, 
however, in Michipicoten Island, which lies about 100 miles southeast of 
the last of the Battle Islands. The following is Logan’s account of Michipi- 
coten Island: 
The strata of which it is composed have a general dip to the east of south, 
and the inclination appears seldom to fall short of thirty degrees. The lower strata, 
towards the north side of the island, particularly as indicated at the upper end, appear 
tobe composed chiefly of amygdaloidal trap, with occasional beds of trap conglomerates, 
red sandstones, and shales; while towards the south these are overlaid by a consider- 
able amount of compact earthy or sub-resinous red trap, assuming sometimes an 
obscure and sometimes a distinct porphyritic character, by the display of ill-defined 
erystals of red feldspar or well-marked erystals of transparent colorless quartz. 
Along nearly the whole of the south side of the island the trap assumes a more 
resinous aspect, and, its color becoming black, it presents the characters of pitchstone 
and pitechstone porphyry. Some of the beds associated with these are of an amygda- 
loidal character, and exhibit large agate veins, which run chiefly in the direction of the 
strike, but frequently also transverse to it. 
