126 THE ROYAL SOCIETY OF CANADA 
LocAL GEOLOGY OF THE BASIN. 
The following formations occur within the basin or in the face 
of the escarpment which bounds it:— 
Sedimentary Igneous 
Ordovician... «=. Richmond..... Limestone 
tice EE RTE Shale 
Trenton... Sa: Limestone 
Pre-Cambran "Roberval. isc clase oe Granite and gneiss 
SAGTIENAY. MS LA Ne dent Are Anorthosite 
Maurentian. £2205 SL pe ARTS Gneiss 
Grenville...... Crystalline limestone 
Laurentian. The Grenville comprises only two small patches of 
a few hundred square feet on the front of theescarpement. The other 
formations occur in larger areas, and all are frequently covered by 
superficial deposits of quarternary age, which are not specified in the 
above list. Laurentian gneiss is therefore, the oldest formation 
that is present in large development. Both dioritic and granitic 
phases appear, and wherever seen it is intensely metamorphosed. 
It presents the usual characteristics of this great system and calls 
for no special description for the purposes of this paper. 
Saguenay. The anorthosite is part of the great development 
of this peculiar rock, which has been fully described by Dr. F. D. 
Adams! under the name of the Saguenay area. It consists essentially 
of basic plagioclase, with subordinate augite, hypersthene, olivine 
and hornblende. Prior to Dr. Adams’ investigation, the anorthosite, 
in accordance with the theory of the sedimentary origin of many cry- 
stalline rocks then in vogue, was regarded as an upper member of the 
Laurentian, overlying the gneisses in stratigraphic sequence. Dr. 
Adams’ researches, however, showed conclusively that the anorthosite, 
here, as in other localities, is an igneous rock, and is here intrusive 
in the Laurentian gneisses, and consequently is of later age. As 
it does not occupy a distinct position in the stratigraphic succession, 
the previously assumed upper Laurentian was thus proven not to 
exist. The total area occupied by this formation in the Saguenay 
district is known to be more than 5,000 square miles. The part of it 
this is contained in the basin of Lake St. John is little, if any, more 
than 200 square miles. Certain portions of this are notable for the 
large deposits of titaniferous magnetite found in them, which, it is 
confidently hoped, the advance of metallurgical science will soon 
render useful. 
1 Ueber das Norian oder Ober-Laurentian,’’ Neues Jahrbuch fiir Mineralogie, 
etc., Bd. VIII, Stuttgart, 1893. 
