360 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
This structure was intruded into overlying rocks, some of which may 
have been post-Lower Huronian and which have since been eroded away. 
It has broken the continuity of the conglomerate, the arkoses and possibly 
the iron formation, leaving remnants of these formations to the east and 
west of it. It is possible that the conglomerate and arkose completely 
covered this mass at one time, but its intrusion into these formations so 
weakened them that they have been easily removed by erosion. In the 
field this rock is readily mistaken for gabbro, but as the specimens of it 
give fairly good thin sections, it is easily recognized under the micro- 
scope as an Olivine diabase so characteristic of the Keweenawan rocks 
of the Nipigon region as well as of these in other parts of Ontario. The 
thin section shows a well developed poikilitic structure with the augite 
crystals enclosing slender, lath-shaped crystals of plagioclase, poly-syn- 
thetically twinned. Much of the augite gives very low polarization colours 
these frequently being grey or drab. Besides the plagioclase and augite 
which make up the larger part of the rock there are small amounts of 
secondary hornblende, magnetite, biotite and olivine, the latter generally 
‘ changing to serpentine. There is absolutely no quartz in the section 
examined and this would be another example in favour of the principle for 
which Rosenbusch has so long contended in spite of examples which 
definitely proved his contention wrong, viz., that it was chemically im- 
possible for quartz and olivine to form together from the same rock magma. 
oe | THE PLEISTOCENE PERIOD. 
The work of the glacier is much in evidence in the Wendigokan 
district. The results of its work are shown in the hills of terminal moraine, 
the long ridges of stratified drift, the stretches of swamp and the broad 
_sand plains. Associated with these deposits there are numerous boulders, 
and west of Lake Wendigokan there are some which contain hematite, 
and one was found containing banded silica and pyrite, the latter being 
very much like some of the iron formation about fifty miles to the north 
and it probably came from that locality. Around Clear Lake the mor- 
ainic hills are very conspicuous, and south of Wendigokan some large hills 
composed largely of moraine, but partly of rock, reach an elevation measur- 
ed by the aneroid, of 240 ft. In the latter district there are beside the 
irregular morainic hills, some long ridges which are not traced out care- 
fully, but on account of their partly stratified structure and serpentine 
outline, appear to be eskers. One of these serpentine ridges crosses the 
north and south line along the west side of claim HF 16 and extends in a 
general northeast and southwest direction. A number of other ridges 
in the region, if studied closely, might prove to be eskers, but little time 
