190 ROYAL SOCIETY OF CANADA 
Although in many instances, and in limited areas, the succession of 
such irruptions can be ascertained with tolerable accuracy, any attempt 
to correlate this succession in detail over extended areas has invariably 
ended in more or less complete failure.” 
The Grenville Series includes a small quantity of altered sediments, 
chiefly limestones. The Hastings Series consists of thinly bedded lime- 
stones and dolomites “ cut through by great intrusions of gabbro, diorite 
and granite.” 
In the Nipissing and Temiscaming regions more recently studied 
both in their field as well as petrographical or microscopical characters, 
the Laurentian rocks are divided by Dr. Barlow into two groups, as 
follows :— 
IL An acidic group: consisting of those foliated rocks similar in 
composition to granites, .etc., to which they correspond, their differ- 
entiation being determined solely by their foliated texture, which, 
usually pronounced, is sometimes obscure and occasionally altogether 
absent. 
“JI. A basic group: These rocks occur interbanded with the more 
acidic gneisses and represent either basic segregated portions of the 
granite magma, or foliated basic irruptives allied to diorites, diabases, 
etc., caught up in it.” 
In a careful petrographical study of the rocks of the Laurentian 
in this area, Dr. Barlow, in conjunction with Mr. W. F. Ferrier, have 
recognized seven groups of acidic gneisses, besides two varieties of: basic 
or hornblende gneisses. 
Except in limited and isolated basins, throughout the length and 
breadth of Ungava and Quebec as well as Labrador—forming the 
Labrador Peninsula and the right limb of the great V-shaped Pro- 
taxis upon which the Post-Archæan sediments were laid—Mr. A. P. Low 
has recognized Laurentian and Huronian rocks, in his numerous 
traverses. 
To the west of Hudson bay, there is, according to Mr. J. B. Tyrrell, 
an extensive and undifferentiated mass of granites which represents in 
the main the fundamental gneisses of the southern part of the great 
Canadian Protaxis. They consist of granites and gneisses and other 
crystalline rocks which are similar in structure and chemical composi- 
tion to the fundamental gneisses (typical Laurentian) and newer crystal- 
line limestones (probably equivalent to the Grenville series) in the same 
portion of Canada. Northward, in the Athabasca lake and Churchill 
river basins, Tyrrell has also recognized Laurentian rocks which he 
describes as granitoid gneisses, hornblende and mica-granites, gabbros 

