[COLEMAN] CLASSIFICATION OF THE ARCH HAN 141 
but this appearance is due to sheared dikes of porphyry or felsite sent 
off from the Laurentian gneiss, which has an eruptive contact some 
distance north. 
In many localities then the Laurentian is in eruptive contact with 
the upper Huronian and, therefore, later in age, while in one or two 
places the evidence seems to make it earlier. Can the two relation- 
ships be harmonized ? 
If we suppose the solid basis on which the Huronian was laid 
down to have had the composition of the gneiss of the Laurentian, 
and suppose further that this basement was fused, or at least, ren- 
dered plastic, by the ascent of the isogeotherms due to blanketing 
with a thick layer of overlying sediments, we may, perhaps, conclude 
that in cases where the conglomerate passes down into unchanged Lau- 
rentian breccia, the mass of sediments happened to be too small to 
raise the underlying rock to the temperature of igneo-aqueous soften- 
ing or fusion. In such localities, we should naturally expect the 
upper Huronian to be much less metamorphosed than elsewhere, and 
this really appears to be the case. 
There is, of course, another possibility, viz., that the quartzite 
at Baie des Pères is later in age than the upper Huronian, Animikie, 
for instance, and not really Archean. It is, however, very much like 
the quartzites of other regions held to be undoubtedly Huronian, and 
has little resemblance to the Animikie of Thunder bay. 
Lawson in his latest treatment of the subject places the Huronian 
(Upper Keewatin) above the Laurentian with an unconformity 
between.’ I have no doubt, however, that in most cases the reverse is 
correct. 
THE RELATION OF THE HASTINGS AND GRENVILLE SERIES TO THE 
HURONIAN. 
The next problem is the relationship of the Hastings and Gren- 
ville series to the Huronian. We may consider the two together since 
the Grenville is now held to be only a more crystalline phase of the 
Hastings series. The Hastings series with its schist conglomerates 
and limestone bands is suggestively like the upper Huronian of the 
west; and the quartzite of the Grenville suggests the upper Huronian 
quartzite. On the other hand, the gneisses of the Grenville, which 
Adams has shown have the composition of slates, come nearest in 
character to Lawson’s Coutchiching gneiss, supposing it to be somewhat 
more completely metamorphosed than it is in the west. 

? Univ. Cal., Bull. Dep. Geol., Vol. 3, No. 3, p. 61. 

