85 
American continent, with an attendant northward reces- 
sion of the coast-line, which began in Upper Cambrian 
time. 
In the western part of the district under consideration, 
Palzeozoic sediments occur south of the Ottawa river, with 
only a narrow strip along the northshore, while in the 
eastern part a broader band of them separates the Pre- 
Cambrian margin from the Ottawa. They lie in almost 
the same attitude as when they were laid down, having 
a slight dip to the south or south-east. Further to the 
south-east, intense folding has taken place in Palzozoic 
and later times, but in this region, where the Palzozoic 
may be regarded as a very thin cover on the Pre-Cambrian 
floor, the latter is responsible for the absence of folding. 
The Pre-Cambrian acted as a buffer against which the 
Appalachian folds were thrust, and suffered no folding 
itself, consequently the thin Palzozoic crust on its surface 
remain untilted. Nevertheless the Palzozoic rocks have 
suffered from dislocation, faults being traceable sometimes 
for long distances across country; for example, the Hull 
and Gloucester fault, mentioned below. In the vicinity 
of Ottawa the Paleozoic rocks are much broken up by 
faults. 
Pleistocene and Post-Pletstocene—A _ great hiatus 
exists between the Palzozoic and Glacial periods in this 
part of Canada. For the greater part of the time repre- 
sented by this hiatus the region formed a part of the land 
surface of North America. The Glacial period has left 
its record in the boulder clay, which has the usual char- 
acters of this rock, and which does not allow of any sub- 
division in this area. Subsequent to the retreat of the 
ice, but while large masses of ice still covered the country 
to the north and maintained an arctic climate, the lower 
part of the St. Lawrence valley was below sea-level. 
This was probably due to the weight of the great bodies 
of ice, still existent to the north. The sea occupying this 
estuary extended almost as far as Kingston. An arm 
extended down the Champlain valley, probably connecting 
with the Atlantic by way of the Hudson valley. Another 
arm reached up the Ottawa river beyond Ottawa. This 
arm had smaller bays running up the Gatineau, Lievre, 
and Nation rivers and other tributaries of the Ottawa 
river. Into this marine arm was emptied large quantities of 
‘“‘rock-flour’’ brought by the streams from the ends of 
