[BLLS & BARLOW] PROPOSED OTTAWA CANAL 181 
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have been their origin however, the alteration into the gneissic and 
crystalline condition must have been completed prior to the deposition of 
the sedimentary Cambrian or other rocks which now rest upon them, 
since in the case of the Potsdam formation, and, in fact, of many of the 
beds of: the lower Cambrian, there is but small indication of a gneissic or 
crystalline structure, except where this has been produced directly 
through local causes. That there has been a subsequent crystallization or 
metamorphism, even in the crystalline limestone of the Laurentian, is 
clearly evidenced by the presence of intrusive masses of diorite, syenite 
or granite which have developed crystals of mica, graphite and other 
minerals along the line of contact. Through the same cause also the 
limestone itself in places is changed to an ophicalcite by the formation of 
grains of serpentine through the crystalline mass. 
While it is now clearly established that some portions of the igneous 
rocks of the Laurentian area, as developed in the area along the Ottawa, 
are of more recent age than the crystalline limestones which are supposed 
to constitute the upper member of the series, certain other portions 
are undoubtedly older, and these most probably represent the lowest 
portions of the earth’s crust known to us. These oldest gneisses are 
foliated rather than stratified ; but in their foliation they underlie the 
regular series of stratified hornblende and other gneisses which occur 
frequently between the fundamental gneiss and the crystalline limestone 
and quartzite series at the summit of the sections. To this fundamental 
series may be assigned the rocks of the Trembling Mountain which were 
assumed by Logan to constitute the lowest member. Similar rocks occur 
as anticlinals north of Lachute, and at different places throughout the 
Grenville district, while large areas occur at various points along the 
upper Ottawa river section. Concerning much of the intermediate 
gneisses, it may be said that while in their general aspect they resemble 
stratified sedimentary rocks, their study under the microscope shows them 
to have presumably a different origin, so that it is possible that the true 
altered aqueous portion may be confined to the areas of crystalline lime- 
stone with their associated bands of quartzite and grayish quartzose and 
hornblende gneiss. But concerning this latter series it must also be said 
that a considerable diversity of opinion already exists, some regarding 
the sedimentary origin of these rocks even to be an open and doubtful 
question. 
The crystalline limestones are particularly developed in the Ottawa 
River section from the vicinity of the Deschénes Lake, west of Ottawa 
city, to the village of Bryson. Here they form a tolerably continuous 
belt extending along the river for many miles, though their continuity is 
frequently broken by the presence of large areas of intrusive granitic and 
dioritic rocks. This portion of the section would, therefore, appear to 
represent the highest members of the Laurentian proper, and at one 
