346 TRANSACTIONS OF THE CANADIAN INSTITUTE. [Vou. VIII. 
intimate mixture of the iron carbonate with the constituents of these 
rocks, though in a loose rock of this sort the waters would have free access 
to the internal spaces and could easily deposit the chemicals at a later 
date. The materials which were laid down as here described gave rise 
when metamorphosed to the carbonate schists. 
It is probable that later the attitude of the land to the sea changed 
still more, and that deeper water covered the rocks so that purer chemical — 
deposits of iron compounds and silica were formed, giving rise to the iron 
ranges, which have since their formation been subject to much meta- 
morphic action. These sediments seem to be the latest of the Keewatin 
system, though in my previous articleon the iron ranges of this region* 
I stated that the more extensive outcrops of the arkoses should probably 
be placed in this system. From further study of these rocks outside of 
this particular district I concluded that they belong to a later system: 
After the Keewatin system was complete, great folding and meta- 
morphism of the rocks took place, forming schists by crushing and shear- 
ing, and the region emerged from the sea so that it was again subject to 
erosion. It is probable that the intrusion of the Laurentian rocks was 
responsible for much of this dynamic action. These rocks are scarce 
in this district, being only seen as a few small dikes, unless there belong 
with them the quartz diorites whose age is by no means certainly known 
and which are rather widely scattered in the region; but the Laurentian 
rose much more prominently to the north and south. 
At the close of the Laurentian period of eruption great erosion of the 
land surface occurred, and after a period the sea again transgressed on 
the land. The materials worn from the surface were then laid down on the 
Keewatin and Laurentian rocks as conglomerates and other mechanical 
sediments, the coarse conglomerates being formed along the coast and the 
less coarse farther out to sea. Probably some of the arkose found quite 
commonly in the district, and just south of the most important band of 
conglomerate, was formed contemporaneously with the latter. If the 
~ sea at the end of the erosion period which succeeded the formation of the 
Laurentian rocks encroached upon the land, on the surface of which 
there was much fragmental material, as there probably would be after 
a period of dynamic action like that of the Laurentian, the water would 
sort this, depositing the coarser near the shore and the finer in deeper 
water. In this way the conglomerate could be formed and if the less 
coarse material suffered comparatively little from the water action it might 
* Report of the Bureau of Mines, 1907. 
