178 ROYAL SOCIETY OF CANADA 
the two great divisions of the Archæan, have ever since been generally 
adopted by workers in this portion of the geological field. 
A description of the crystalline rocks along the Ottawa River section 
and of the country adjacent was given by Sir Wm. Logan in his report 
for 1847. At that time they were regarded as, for the most part, of 
metamorphic origin, the supposition being that they were originally 
deposited like the sediments of later Paleozoic times. The principal 
rock mass was stated to be a red syenitic gneiss, with hornblende and 
mica arranged in a parallel direction. On the Madawaska River, a branch 
of the Ottawa in the south, a section of 1,350 feet was measured, which 
comprised gneiss, crystalline limestone and micaceous quartz rock, in 
which the calcareous members were in three bands and interstratified 
with the gneiss. The whole series at this point presented many of the 
physical features of altered sedimentary strata, and they were supposed 
to conformably overlie the great area of syenitic rocks more especially 
developed to the west. Both series were intersected by clearly intrusive 
granitic and pyroxenic dykes and veins. 
Iu 1852 the series of crystallines north of the Ottawa and St. Law- 
rence was examined, and in 1857 the report of Logan on the areas west 
of Montreal was published. These rocks, consisting of gneiss, limestone, 
quartzite and anorthosite, were all styled metamorphic sediments, follow- 
ing the principles enunciated in the earlier report on the area to the 
west. The presence of eruptives, such as syenite, porphyry, diorite and 
trappean rocks of various kinds, was noted, but all these were regarded 
as older than the Potsdam sandstone, which at various points was observed 
to flank the base of the Laurentian hills. In this series also the anortho- 
sites were considered as being an associated division of the limestones, 
and as possibly belonging, with them, to one great undulating mass. It 
was not, however, till the publication of the Geology of Canada, 1863, 
that anorthosites or Labradorite rocks were stated to form the upper mem- 
ber of the Laurentian series, being there said to probably constitute an 
upper unconformable division to the crystalline limestone, with an approxi- 
mate thickness of 10,000 feet. This area of rocks north of the lower 
Ottawa was styled the Grenville series,’ and was regarded as representing 
most completely the structure of the oldest crystallines of Canada. 
In the meantime Logan’s co-worker, Murray,’ described the usual 
series of gneisses, crystalline limestone and quartzite of the Thousand 
Islands and of the mainland to the north, with associated areas of what 
he regarded as conglomerates, the latter being held to be conclusive evi- 
dence of the sedimentary and metamorphic character of the whole. In 
1853°* he made a traverse from Lake Huron by way of the Muskoka and 
1 Geological Survey Report, W. E. Logan, 1853-56. 
2 Geological Survey Report, A. Murray, 1851-52. 
3 [bid., 1853-56. 
