12 
MUUSEM BULLETIN NO. 18. 
east of Brockville, states that “if faults exist in the district 
their extent must be quite limited 1,1 
THE LAURENTIAN PLATEAU ESCARPMENT. 
The general topographic relations of the Palaeozoic and 
Archaean areas are those of a lowland lying at an average eleva- 
tion of about 1,000 feet below an adjacent plateau whose sur- 
face is irregular, but whose sky-line is, in places at least, exceed- 
ingly even (see Plate I, C). Northwest of Montreal, the surface 
of the Laurentian plateau is estimated by Adams 2 to have an 
average elevation of from 1,000 to 1,500 feet, the adjacent low- 
land standing 100 to 300 feet above tide. North of Quebec 
the summit of Roundtop, which marks the southern border of 
the plateau in that vicinity, attains an elevation of 1,600 feet 
(barometer). Near Ottawa, Kings mountain rises just north 
of the scarp to an elevation of 1,220 feet, the lowland to the south 
having an elevation of from 200 to 300 feet. Many points 
on the plateau a few miles north of its southern border attain 
somewhat greater elevations. In the region north of Ottawa the 
elevation of the plateau at the Hudson Bay divide only slightly 
exceeds that of the higher points like Kings mountain near the 
escarpment. The height of the divide itself, over the area 
covered by Wilson’s® map, generally lies between 1,000 and 
1,400 feet. Farther east the plateau is somewhat higher. One 
of the highest points in this more easterly region is Trembling 
mountain, 2,380 feet, which is located about 35 miles north of 
the southern border of the plateau. 
The small topographic map, Figure 1, represents an area in 
the lower Ottawa valley where the typical relations of the north- 
ern border of the Palaeozoic lowland and the Laurentian plateau 
are shown. This representative bit of topography shows the 
almost perfectly flat Palaeozoic plain meeting the steep scarp 
face of the southern margin of the Laurentian plateau in a 
nearly straight line. Along portions of the escarpment the con- 
1 Trans. Roy. Soc. Canada, vol. 6, sec. 4, 1900, p. 118. 
2 Ann. Repl. Geol. Surv., Canada, new ser., Vol. VIII, 1894 (1897), p. 8J. 
! Geol. Surv., Canada, Mem. 4, 1910. 
