In discussing the structure of the Laurentian rocks, as developed in the valley of the Ottawa river, their characteristics, as given in the first report of the late Sir William Logan, in 1845–’46, on “The Laurentian of the Upper Ottawa,” may here be presented. After stating that a low anticlinal crosses that river between the mouth of the Mattawa and the foot of Lake Temiscamingue, he says:
“The lowest rocks which this undulation brings to the surface are of a highly crystalline quality belonging to the order which in the nomenclature of Lyell is called metamorphic instead of primary, as possessing an aspect inducing the theoretic belief that they may be ancient sedimentary formations in an altered condition. Their general character is that of syenitic gneiss. Their general color is reddish, and it arises from the presence of reddish feldspar, which is the prevailing constituent . . .