608 G. M. DAWSON ON THE SUPERFICIAL GEOLOGY OF 



also follows that of the ice-action, it is at the same time that of the 

 belt of Huroniau rocks already mentioned. The course of the 

 glacial striae is extremely uniform, and, from a great number of 

 observations in different parts of the lake, is found to vary through a 

 few points only, lying between north-north-east and south-south- 

 west and north-east and south-west. Slight deflexions, sometimes 

 observed, are generally tiaceable to deviation of the ice by masses 

 of resistent rock running athwart its course, the striae always 

 showing a tendency to bend towards the more level regions, and 

 away from the more elevated and rugged parts. 



At a few places in the southern part of the lake, glaciation in the 

 ordinary direction which gives form to the rock masses, was observed 

 to be superinscribed with coarser scratches nearly east and west in 

 direction. Some of these may be due to the packing of the ice of 

 the lake itself in the spring ; but instances occur which cannot be 

 accounted for in this way. Some rock-surfaces on a low promontory 

 in the southern part of the lake afford interesting examples. The 

 most important direction and that with which the forms of the sur- 

 face coincide is here S. 13° W., superimposed on which at one place 

 are scratches S. 45° W. or N. 45° E. Near this a direction of S. 

 50° W. or BT. 50° E. occurs, on which is superimposed striatum 

 S. 15° W., a direction closely agreeing with the general one, and 

 probably indicating a brief resumption of the original force after a 

 short interval. 



Many interesting special cases showing the character and effect 

 of the glacial action, came under observation ; but with these I do not 

 wish to burden this paper. The nature of the present outfall of the 

 lake, however, deserves mention. There are two channels now in 

 use, and evidence of at least one other now disused. They cross a 

 narrow ridge which separates the waters of the lake from those of 

 the basin -like head of the Winnipeg River, and are comprised 

 within a distance of about two miles. The hard ridge marks the 

 junction by fault of the Laurentian and Huroniau rocks, the line 

 nearly following its crest. The gaps through which the water 

 flows do not depend on any evident peculiarity of geological struc- 

 ture, but probably owe their origin to smaller transverse faults or 

 joints, as a fissure filled with a large greenstone dyke was observed 

 not many miles distant with a direction parallel to theirs. The 

 gorge-like gap through which the northern stream flows is the 

 most interesting, and was most carefully examined. It is occupied 

 by a very picturesque cascade, the first leap of the Winnipeg River. 

 It is certainly preglacial in date, and has probably arisen from 

 subaerial weathering along some line of weakness. The glacial 

 striae cross over it obliquely at an angle of about 30° with its 

 direction ; and the ice has had wonderfully little effect on its shape, 

 having only succeeded in rounding off somewhat the exposed angles 

 of the cliffs. Since the glacial period the river has done little, as 

 the rocks retain their rounded aspects and show ice-striation almost 

 everywhere. 



