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BULLETIN OF THE LABORATORIES 
several of the recent writers on the geology of Lake Superior have 
given such collations and discussions from their several points of view, 
notably Wadsworth, in “The Azoic System and its subdivisions”, 
1884, and Irving, in his “Copper-bearing rocks of L. Superior”, 
1885. Recent discussions may also be found in the Annual Reports 
of Minnesota. In the region in question the geological relations ap- 
pear to be relatively simple, but at the same time so intimately associ- 
ated with the more intricate regions now chiefly under discussion as to 
make any conclusions which can be reached of considerable value. 
In general then, the region northward from L. Superior is a part 
of the great V-shaped area of crystalline rocks classed as Azoic and 
usually grouped in two great series, the one largely composed of 
gneisses and granites and called Lawrentian, and the other, assumed to 
be higher (and hence later) composed of crystalline slates and schists. 
This whole series is supposed to consist of altered sediments, but with 
an unconformity between the two groups. The evidences of life are 
restricted to those furnished by the exceedingly problematical Eozoon 
and the presence of graphite and iron. The original name given to 
both these members was the term Azoic, applied by Foster and Whit- 
ney, in 1850. Whitney and Wadsworth vigorously assert that there 
exists no reason for changing this name (as to Archean) or subdividing 
the series (into Lawrentian and Huronian). The Canadian geologists 
claim that the Huronian schists are constantly unconformable to the 
underlying Lawrentian and frequently contain pebbles from it. To 
this Wadsworth and Whitney reply that there is a lack of observation 
to substantiate the claim of unconformability and that the pebbles are 
high in the series of the Huronian and not in any sense basement con- 
glomerates. At page 557 of the “ Azoic System,” these authors seem 
to imply that the Huronian conglomerates are formed by the imbed- 
ding of matter ejected in a fragmental state in a detrital magma. 
In the region under consideration a further difference of opinion 
seems to prevail. Irving, in the map of L. Superior, given in his val- 
uable report on the “ Copper-bearing Rocks,” marks all the granitic 
areas as Lawrentian and the schists as Huronian, while the Canadian 
geological map indicates all the granite areas near the lake and associ- 
ated with the schists as eruptive, although a region to the north is cov- 
ered with the Lawrentian. In the sequel the evidence which leads us 
to accept the conclusions of the Canadian geologists as to this particu- 
lar region, is reviewed in detail so far as our material warrants. 
