42 A. B. WILLMOTT 



the west of the line is much lower than that to the east of it, and 

 is separated from it by a deep valley. The Keweenawan to the 

 east of the line on Lake Nipigon is a shallow overflow. The 

 physical features of this line are thus similar to the others, but 

 with the characters less marked, due probably to the fading 

 out of the force-producing dislocation. 



Eastward from the St. Lawrence the contact seems to run 25° 

 S. of E. and then east. With this region I am not personally 

 familiar, but believe that here also the Archaean rises in steep 

 hills above the adjoining, low-lying post-Archaean. 



The two facts brought out above, viz., the step-like regularity 

 of the lines of contact, and the difference in altitude of the rocks 

 of the two periods, can be best explained, I believe, by assuming 

 a dislocation in the Archaean before the deposition of the post- 

 Archaean sediments. The southern part was depressed and 

 probably changed in inclination, as suggested by Wilson in 

 the paper quoted above. Sediments were deposited over this 

 depressed part and abutted against the cliffs of the northern part. 

 They also extended into the deeper valleys of the northern part. 

 Perhaps even a considerable portion of the northern part was 

 thinly covered, but, if so these rocks have since been removed. 



The regularity of the dislocation extends from longitude 75° 

 to longitude 88°, and from latitude 43° to latitude 50°, or for 700 

 miles by 500. For the greater part of the distance this line of 

 fracture forms the northern and eastern shores of Superior and 

 Huron. 



A. B. WiLLMOTT. 

 Sault Ste. Marie, Canada. 

 January 21, 1904. 



