16 
MUSEUM BULLETIN NO. 18. 
authors consider to represent a fault line scarp. 1 Post-Cam- 
brian faulting appears to be the only inference which accords 
fully with all the evidence. The escarpment is located along 
the northern border of a zone in which subsidence faulting is 
known to be a common and characteristic structural feature. 
The character of the topography along the southern border of 
the Canadian shield north of the St. Lawrence and Ottawa 
valleys is quite different in character from that along its western 
border. Along the shores and on the islands of the southern 
half of Lake Winnipeg the Palaeozoic and Archaean rocks ap- 
proach each other rather closely for nearly a hundred miles, 
but the latter shows little if any greater relief than the former. 
Archaean rocks form the eastern and Palaeozoic rocks the western 
shore of this long shallow lake throughout its entire length of 
250 miles. Along the eastern border of Lake Winnipeg, the 
Archaean generally occurs in the form of low rounded knobs 
of granite, few of which rise more than 50 feet above the lake. 
At the north end of the lake the actual contact of the two sys- 
tems is covered by drift, but the general level of the western- 
most exposures of the Archaean, near Warrens Landing, is lower 
than that of the near-lying easternmost exposures of the Palae- 
ozoic. In the region still farther north and northwest, geologists 
familiar with the country report a similar absence of marked 
topographic discordance between the areas underlain by Palae- 
ozoic and Archaean rocks. Outside of the Ottawa and St. 
Lawrence Valley region any escarpment is apt to be on the Palae- 
ozoic side of the contact. The Archaean-Palaeozoic contact, 
which extends west from Kingston to Georgian bay, shows the 
same topographic contrast with the Laurentian Plateau escarp- 
ment as the one just described between the latter and the west- 
ern border of the Archaean. Here the uniform relations of 
Pre-Cambrian highland and Palaeozoic lowland found north 
of the Ottawa and St. Lawrence rivers are often reversed, for 
the Ordovician limestone frequently forms a more or less pro- 
nounced cliff overlooking a Pre-Cambrian area of less relief. 
1 The reader is referred to a paper by Prof. W. M. Davis (Science, 
N. S., vol. XXVI, pp. 90-93, 1907) for a discussion of the terms fault scarp 
and fault line scarp. 
