110 ROYAL SOCIETY OF CANADA 
neither the base nor the upper part of the formation. From other out- 
crops in this area, however, it is conjectured that there are here about 
320 feet of the sandstone between the Archean and the base of the 
Calciferous. Near Beauharnois a thickness of fifty-five feet of the 
sandstone was measured but this did not include either the base or the 
top of the formation. 
As we ascend the Ottawa the thickness of the Potsdam decreases. 
Thus near the village of Quyon, thirty-five miles west of Ottawa, a small 
quarry in this rock is seen underlain by granite, the thickness of the 
sandstone being not more than twenty feet. So far the sandstones of 
the Potsdam have not been recognized west of this place, and near the 
foot of the Chats falls the Calciferous is in contact with the Archean. 
The widespread areas of the Potsdam and Calciferous seen along 
the Rideau river and about the Rideau lakes do not furnish good sec- 
tion for measurement, since the strata are everywhere in a generally 
nearly horizontal attitude, or affected by low undulations, so that all 
estimates as to actual thickness in this district would be largely con- 
jectural. 
The Calciferous formation is estimated to have a thickness of not 
far from 300 feet. As in the case of the Potsdam or lower division a 
full section cannot be measured at any one point and the total volume 
may in places be somewhat greater. Thus in the area between the 
village of Lachute and the Ottawa river, judging from the surface out- 
crops, and assuming the dip of the strata to be constant, the entire 
thickness of this formation would approximate 450 feet. At Rigaud 
village, a small section on the river a la Graisse shows only forty-one 
feet, but the upper part of the formation is concealed by drift., 
In regard to the great display of these rocks in the western portion 
of the basin, it is also as yet impossible to give accurate figures as to 
their thickness. They extend over hundreds of square miles and are 
affected by low folds and sometimes by faults. In places the anticlines 
are well defined and the opposing dips are sometimes as high as twenty 
degrees in the vicinity of the Rideau river, but usually these dips are 
not greater than five degrees. 
The Calciferous rocks are seen at intervals along the valley of the 
Ottawa river as far west as the head of Allumettes island where they 
are overlain by the Chazy shales. They appear on the south side of the 
river in a small exposure about five miles west of Pembroke, but above 
this point have not been recognised. The formations here are evi- 
dently much thinner than in the eastern portion of the basin. 
Throughout the western part of the Ottawa basin, these rocks, 
with their associated Potsdam sandstone, form a broad area, overlying 

