476 A. C. Lawson— Geology of the Rainy Lake, Region. 
the use of this term to imply that the rocks are necessarily of 
the same age as those described as the typical Laurentian by 
Logan, or as those named Laurentian in any other part of the 
world. For it is manifestly at variance with scientific methods 
to definitely correlate, with reference to age, rocks in which 
there are no criteria for comparison other than their petro- 
graphical characters. That the rocks considered have passed 
through a period of fusion and solidification is a palpable fact 
in the Rainy Lake Region, and will probably be also estab- 
lished beyond question in other regions when they come to be 
carefully studied.* 
But to assume that the period of solidification, which defines 
the age of the rock, was the same the world over, is as yet un- 
warranted. If prior to fusion the material was in form of strati- 
form sediments, these may have been of many different ages, 
and may have been fused in different parts of the earth at very 
diverse periods anterior to the deposition of fossiliferous strata.’ 
If it constituted, prior to fusion, the first formed crust of the 
globe, the period of fusion might, as before, be very different in 
different regions before the advent of life upon the surface of 
the earth. The loose way in which the term Laurentian is 
used is convenient in the present state of science, but let it be 
clearly understood—as it is not generally—that the usage is 
different from that familiar in the fossiliferous formations. It 
is in this loose sense—the strictest permissible in the present 
state of science—that these rocksare referred to the Laurentian. 
Superimposed upon the rocks thus referred to the Laurentian 
system, the splendid exposures of the shores of Rainy Lake 
reveal as the next geological group a thick series of very dis- 
tinctly stratiform mica schists and fine grained, gray, evenly 
bedded, often garnetiferous, very quartzose eranulitic-gneisses. 
The use of the same term “ gneiss” both for the foliated modi- 
fications of granites and syenites which are clearly of igneous 
origin, and for bedded rocks of similar composition to the oran- 
ites, but whose natural history has evidently been very differ- 
ent, is very confusing. The lack of distinction in terms has 
been fruitful of much error. The term gneiss is coming more 
and more to be used by geologists to describe a certain phase of 
structure independent of composition. The fine-grained bed- 
ded gneisses often have the character of granulites “when exam- 
* Wadsworth has already called attention to the fact that the foliated granite 
of the Marquette district, described by Brooks and other geologists as Laurentian, 
is of more recent age than the rocks there referred to the Huronian and the 
intrusive nature of the contact is described. Vide Notes on the Geology of the 
Tron and Copper Districts of Lake Superior, Bull. Mus. Comp. Zool., Harvard, 1880, 
p. 52 et seq., p. 70 et seq. The work was not known to me when I described the 
Contact of the Laurentian and Keewatin of the Lake of the Woods, Annual Report, 
Geol. Survey of Canada, 1885. 
