STRUCTURAL RELATIONS OF PRE-CAMBRIAN AND PALEOZOIC. 
9 
Trenton lies nearly 1,000 feet below sea-level. This gives a 
difference in the present altitude of the base of the Ordovician 
rocks at Clear lake and Toronto amounting to about 1,800 feet. 
If the Ontario Archaean shield, extending from the Lake Nipissing 
district to the head of the St. Lawrence, antedates Palaeozoic 
sedimentation in origin, the remnants of these sediments now 
found near its centre should be of much later age than those 
which lie around its margin; but, as shown by the Clear Lake 
outlier, this is not the case. The only inference which can be 
drawn from the known facts of areal distribution and age of the 
sediments in this region is that the Nipissing-Kingston uplift 
is of late Palaeozoic or Post-Palaeozoic origin. 
The Palaeozoic plain of the Ottawa and St. Lawrence valleys 
lies between the Laurentian plateau on the north and the Adiron- 
dack uplift on the south, and extends eastward from the Archaean 
shield at the head of the St. Lawrence to the zone of Appalachian 
folding east and southeast of Montreal. 
The Palaeozoic sediments which underlie the surface of this 
plain over a considerable part of the area have a thickness of 
from 2,000 to 3,000 feet, a section which probably represents only 
a fraction of the original thickness of the Palaeozoic. Indeed, the 
remnant of Devonian rocks at Montreal 1 and various outliers 
of the Palaeozoic furnish conclusive evidence of this fact. 
Subsidence or normal faulting is a structural characteristic 
of the Palaeozoic rocks throughout the northern part of this low- 
land. Numerous faults, of which the one at Montmorency falls 
with a throw of 600 feet 2 is an example, are present in the eastern 
part of the region. In the Ottawa valley the sedimentary rocks 
are cut by numerous faults, many of which have been described 
by Ells 3 and shown on maps of the Geological Survey, Canada. 
Various other faults, some of which have considerable lateral 
extent, are known to the writers, and many minor faults are 
1 Harvie; Canada, Roy. Soc., Proc. and Trans., 3d. sen, Vol. 3, sec. 4, 
pp. 249-299, 14 pis., 3 figs. 1910. 
2 Raymond; Int. Geol. Cong., Geol. Surv., Canada, Guide Book No. 1, 
1913, p. 40. 
* The physical features and geology of the Palaeozoic basin between 
the Lower Ottawa and St. Lawrence rivers, R. W. Ells, Trans. Roy. Soc. 
Canada, Vol. 6 , Sec. 4, pp. 99-120, 1900. 
