THE CENTRAL REGION OF NORTH AMERICA. 607 



the first clear definition of the three steppes into which the interior 

 region of British North America is naturally divided. 



The region which has come under my own observation is for the 

 most part pretty closely confined to the forty-ninth parallel, and forms 

 a line about 900 miles in length, extending completely across the 

 interior plateau of the continent. 



Glacial Phenomena of the Laurentian Axis, 



Beginning, then, with the glacial phenomena of the Laurentian 

 axis, I shall describe the appearances presented in the neighbour- 

 hood of the Lake of the Woods only, where this axis is intersected 

 by the forty-ninth parallel ; but, from the similarity of the traces 

 of glacial action even in very distant parts of the Laurentian 

 region, this will serve in some sense as a representation of its general 

 features. 



The Lake of the "Woods, as a whole, occupies a depression in the 

 south-western slope of the Laurentian region (see Map, PL XXXIL). 

 It is over 70 miles in extreme length, and has a coast-line of between 

 300 and 400 miles. Its northern part is comparatively deep, reaching 

 in some places a depth of over 80 feet. Its general form has been 

 determined by that of an area of less highly altered rocks, which are 

 probably Huronian ; and the details of its outline even follow very 

 closely the changing character of the rock, spreading out over the 

 schistose and thinly cleavable varieties, and becoming narrow and 

 tortuous where compact dioritic rocks, greenstone conglomerate, 

 and gneiss prevail. Its shores are almost invariably composed of 

 solid rock with the rounded forms characteristic of ice-action, and 

 dip rapidly below the surface of the water, forming a bold coast, 

 sandy or gravelly beaches being comparatively rare. It is studded 

 with innumerable islands, few of which are laid down on the im- 

 perfect maps yet made of the region, but which vary from those 

 several miles in length to mere water-wasted rocks. The islands, 

 like the mainland, are seen, where not covered with luxuriant vegeta- 

 tion, to be composed of round-backed rocks. Only where the rocks 

 are of a specially soft or schistose character has the action of the 

 waters of the lake had sufficient effect on them to form cliffs. The 

 southern part of the lake is very different : there are few islands ; 

 the water is not deep ; and the whole southern shore is formed by 

 low-lying deposits of sand and detrital matter, Where rock-surfaces 

 appear, however, they are like those of the northern part of the lake, 

 heavily glaciated. 



All the harder rocks of the region still show with the utmost per- 

 fection the scratching and grooving of the glacial period ; and some 

 of the more compact granites and intrusive diorites retain a surface 

 still perfectly bright and polished. On a small scale even the hard- 

 est and most homogeneous of the rocks show a tendency in the 

 longer axis of their elevations to parallelism with the glacial mark- 

 ings. Though the general direction of the northern part of the lake 



Q. J. GL S. No. 124. 2 s 



