24 THE ROYAL SOCIETY OF CANADA 



districts, the highland border in this region is comparatively gently 

 sloping the regional gradient of the Pre-Cambrian surface being 

 generally not more than 20 to 50 feet per mile. 



In those portions of the highland border that are gently sloping, 

 outliers of Palaeozoic strata belonging to the same formation occur 

 scattered over the surface of the Pre-Cambrian. It is obvious there- 

 fore that in such localities at least a fault of considerable displacement 

 could not be present. 



Conclusions 



The region lying along the southern border of the Laurentian 

 plateau to the north of the lower Ottawa and St. Lawrence valleys is 

 of special interest to the geologist because, perhaps more than any 

 other locality, it affords an opportunity to study the relationships of 

 the early Palaeozoic formations to the Pre-Cambrian of the Canadian 

 shield and from these relationships to infer the extent of the Palaeozoic 

 submergence over the eastern part of this ancient land mass. The 

 purpose of the present paper has been to briefly summarize the avail- 

 able data bearing on the relationships of the Palaeozoic to the Pre- 

 Cambrian in this region, and from these data to draw whatever con- 

 clusions they seemed to warrant. These conclusions briefly stated 

 are twofold (1) that the present relationships of the Palaeozoic to the 

 Pre-Cambrian along the southern border of the Laurentian highlands 

 in southeastern Ontario and the adjacent portions of Quebec have been 

 brought about by a combination of three factors; (a) the deposition 

 of the early Palaeozoic formations, Potsdam, Beekmantown and 

 Chazy in a broad depression extending over a large part of the region 

 now included in the lower Ottawa and St. Lawrence valleys; (b) the 

 downwarping or downfolding of the Palaeozoic formations along the 

 whole southern border of the Laurentian plateau; and (c) the down- 

 faulting of the Palaeozoic strata in scattered localities but chiefly in a 

 zone extending along the lower Ottawa river from the Ottawa district 

 eastward to Montreal. 



(2) That the southern border of the Laurentian highlands to the 

 north of the lower Ottawa and St. Lawrence valleys, is marked in two 

 localities by abrupt escarpments which probably owe their origin to 

 differential erosion along local fault planes but is not delimited by 

 a through-going fault nor by a fault-line scarp. 



