22 THE ROYAL SOCIETY OF CANADA 



a maximum length in the case of the longest faults of 30 to 40 miles. 

 The displacement along the faults, although it attains a maximum of 

 approximately 1,600 feet in the case of the Hull and Gloucester fault, is 

 generally considerably less than this amount and usually decreases by 

 several hundred feet in a few miles in directions away from the point 

 of maximum displacement both along the line of fault and at right 

 angles to the line of fault. It is obvious therefore, that, although 

 faulting has been an important factor in lowering the elevation of the 

 Palaeozoic strata throughout the belt of territory adjoining the 

 Laurentian highlands between the Ottawa district and Montreal, these 

 displacements are local in extent and, quantitatively at least, are 

 relatively the least important of all the factors by which the present 

 relationships of the Palaeozoic to the Pre-Cambrian in southeastern 

 Ontario and the adjacent portions of Quebec may be explained. 



Origin of the Eardley and Grenville Escarpments 



That the Eardley and Grenville escarpments probably owe their 

 origin to Post-Ordovician faulting evidently suggested itself long ago 

 to the officials of the Geological Survey engaged in field work in the 

 Ottawa valley, for, on a map of Ottawa county prepared by Vennor 

 and published in the Report of Progress of the Geological Survey for 

 1876-77, the Eardley escarpment is indicated on the margin of the 

 map as a fault. The general data upon which this hypothesis is based 

 are the following ^ : 



The occurrence of the escarpments along the northern edge of an 

 area in which the Palaeozoic strata are intersected by numerous faults 

 having the same average length and parallel trends. 



The occurrence of the escarpments in places on the contact of the 

 Palaeozoic and the Pre-Cambrian. 



The manner in which the escarpments cut abruptly across the 

 structure of the Pre-Cambrian rocks which adjoin them on the north. 



The absence of any change in the lithological character of the 

 Palaeozoic sediments adjacent to the escarpment such as would 

 probably be present if the escarpment were Pre-Palaeozoic in age. 



When engaged in field work in the Grenville district in 1916 the 

 writer examined the base of the Grenville escarpment in favorable 

 localities in the hope of finding outcrops of Palaeozoic in which some 

 evidence favorable to or opposed to the faulting hypothesis might be 

 found, but at that time the only exposure observed in close proximity 



»See Kindle, E. M., and Burling, L. D., Mus. Bull. No. 17, Geol. Surv., Dept. 

 of Mines, Can., p. 23, 1915. 



