214 REPORT ON CORRELATION 
about twenty-five miles to the east of the Morin anorthosite intru- 
sion. This possesses the ordinary character of such granitic rocks. 
More especially in the southern portion of the “original Lauren- 
tian area’’ there also occur a great number of basic dikes, consisting 
for the most part of diabase, which represent, as a general rule, the 
latest intrusions of the district, and which persist across the front 
of the whole area from west of Grenville to a point north of the 
island of Montreal, where they disappear beneath the Ordovician 
cover. These diabase dikes were, however, considered by Logan 
to be older than the intrusion of syenite in the Grenville district 
already mentioned, which, in its turn, was older than the porphyry 
intrusion which cut it. While, therefore, in this original Laurentian 
area and its eastward extension there is not so great a relative pro- 
portion of rocks which are clearly of intrusive origin as in the case 
of the Adirondack area, intrusive rocks in very considerable variety 
and of the same general types are represented. 
It is worthy of mention that in the Laurentian protaxis still farther 
to the east, in the district to the north of the Gulf of St. Lawrence and 
in the Labrador peninsula, a number of anorthosite intrusions of 
gigantic extent occur. Among these may be mentioned more espe- 
cially one which may be referred to as the “Saguenay anorthosite,”’ 
on account of the fact that it is developed about the head waters of 
this river. This, which resembles the Morin anorthosite in char- 
acter, has an area of not less than 5,800 square miles. Another 
enormous area is traversed by the Moisie River, the Clearwater, 
a tributary of the Moisie, running through a great canyon in this 
anorthosite. Still others of similar extent might be mentioned. 
The occurrences of anorthosite which are now known to exist in the 
Labrador peninsula represent a total area of nearly 50,000 square 
miles. ; 
Asa result of his studies in the Grenville region, Logan announced 
his belief that the Laurentian system consisted of two great uncon- 
formable series of sedimentary rocks, to which he gave the names 
“Upper Laurentian” and “Lower Laurentian.” The latter he 
considered to be again divisible into a lower and upper portion, 
which subdivisions he considered to be probably conformable to one 
another. In the course of time these several series came to be known 
