22 
MUSEUM BULLETIN liO. IS. 
points generally lie between 1,000 feet and 2,000 feet. 1 The 
present very moderate relief of the region near the Height of 
Land affords no reason for assuming that the seas of Ordovician 
time may not have extended to the Hudson Bay region. In 
this connexion the suggestion of Cushing, 2 that the Adirondack 
mountains were possibly submerged at the close of Utica sedi- 
mentation, is worthy of consideration. 
The occurrence of outliers of Palaeozoic rocks, some of which 
are far within the limits of the Laurentian plateau, affords 
conclusive evidence of the former wide extent of some of the 
Palaeozoic seas. These include the outliers at Echo lake, Lake 
Nipissing, and at Saguenay. These small areas of Palaeozoic 
limestone may all belong to down-faulted blocks which have 
thus escaped erosion. They appear to have had an origin 
similar to the Wellsville outlier in the Adirondack region, which 
has been down-faulted more than 1,600 feet. 3 They serve 
effectively to support the evidence from other sources that the 
Palaeozoic seas extended very widely if not completely over 
the Laurentian upland southeast and east of Hudson bay. 
SUMMARY. 
The Canadian shield or Laurentian plateau in the vicinity 
of the Ottawa and St. Lawrence valleys rises abruptly from the 
comparatively level plain to the south. This physiographic 
feature of the Pre-Cambrian crystallines to which the term 
Laurentian Plateau escarpment is applied, makes a series of 
nearly straight or gently curving lines at its contact with the 
comparatively flat lying Palaeozoic sediments to the south. It 
has been generally regarded as having formed the more or less 
permanent southern shore-line of the Pre-Cambrian nucleus 
of the American continent; but the authors believe that the sea 
floor of the early Palaeozoic was there interrupted by little 
inequality of grade, and that the Palaeozoic seas extended very 
1 Wilson, M. E., Geol. Surv., Canada, Mem. 39, 1913. 
Wilson, W. J., Geol. Surv., Canada, Mem. 4, 1910. 
* Bull. N. Y. State Mus., No. 145, 1910, p. 96. 
* Miller, W. J., Bull. N. Y. State Mus., No. 164, 1913, p. 83. 
