4 
MUSEUM BULLETIN NO. 18. 
A remnant of this formation about 75 feet thick, southeast of 
Ottawa, has escaped complete denudation owing to its occurrence 
along the lower margin of a slightly tilted fault block. This 
Ottawa remnant of the Queenston is about equally distant from 
the outlier northeast of Montreal and the main mass of the forma- 
tion on the south side of Lake Ontario. Both of these outliers, 
which have been preserved from erosion through fortuitous 
structural features, were doubtless originally portions of an un- 
interrupted extent of the Queenston shale across southeastern 
Ontario to the Nicolet River district in Quebec. In both New 
York and Quebec this formation approximates a thickness of 
1,000 feet, and it is probable that it was originally represented by 
a comparable thickness over much of the Ottawa and St. Law- 
rence valleys where it is now entirely absent. 
Concerning the former extent of the rocks of the Silurian 
system over this region nothing is known. The Devonian, 
however, is known to have been present in the Montreal district 
and it is quite possible that the whole Palaeozoic section from the 
Potsdam to the Devonian was present over a considerable part 
of the Ottawa and St. Lawrence valleys. 
THE PRE-CAMBRIAN SURFACE. 
The hummocky or roches moutonn&es character which so 
generally characterizes the Pre-Cambrian rocks was at one time 
usually ascribed to ice erosion. Laflamme was one of the first to 
note that in at least one district near Lake St. John “these de- 
pressions must necessarily have existed at the bottom of the 
Palaeozoic ocean when the limestone beds were being deposited.” 1 
Lawson, a few years later, showed clearly that both the Palaeo- 
zoic and Animikie rested on a highly irregular Archaean surface. 2 
All recent observers appear to agree that the old Pre-Cambrian 
land surface which the Cambrian sea invaded presented topo- 
graphic features essentially similar to those now found in the 
Laurentian areas of southern Ontario which have been recently 
denuded of their Palaeozoic cover. Prof. Cushing, in discussing 
1 Geo!. Surv., Canada, Rept, Prog, for 1882, 3, 4, Pt. D. 
2 Bull. Geol. Soc. America, Vol. I, 1890, pp. 163-173. 
