BEACHES OF LAKE AGASSIZ. 405 



stunted grass and dotted with a few scrubby oak trees. This plain is a 

 delta deposit of a river that flowed into Lake Agassiz when this lake was at 

 its highest stage ; and on the sides of the channel which the present river 

 has since cut through the plains a number of very interesting and instruct- 

 ive sections can be seen, including both the superficial deposits and the un- 

 derlying Cretaceous. 



Beyond the Valley river the ridges continue in a direction 15° west of 

 north for sixty miles, to the northeast angle of the Duck mountain, when 

 they turn abruptly westward into the valley of Swan river. Crossing this 

 valley they are well marked on the eastern face of the Porcupine mountains, 

 north of which they turn westward for a long distance into the vallay of 

 Red Deer river, ending in a wide, flat, sandy delta plain. 



Whether they extend along the face of the Pasquia mountain has not 

 yet been determined ; but the Pas ridge oh the Saskatchewan river would 

 appear, from descriptions we have of it, to be one of these ancient beach 

 ridges, though its elevation is not nearly so great as most of the well defined 

 ridges along the face of the Duck and Porcupine mountains. 



These beaches as a rule are in the form of slightly rounded ridges from 

 > fifty to two hundred feet high, raised from three to twenty-five feet above 

 the surrounding country. They are composed of sand and small water- 

 worn pebbles, a few of which are granitic or quartzitic, while a great ma- 

 jority are of the white Paleozoic limestone at present outcropping around 

 the adjoining lakes. The gravel must, however, have been derived entirely 

 from the till that had previously been carried by the glacier from the bedded 

 rock at a distance, for there is now no known outcrop of these limestones 

 with a greater elevation than about nine hundred and thirty feet, or more 

 than five hundred feet below the summit of the highest of the gravel ridges. 

 Cliffs of till that might furnish sources of supply for the pebbles are also 

 often separated by very long intervals ; so that it is probable that most of 

 the gravel was brought down by rapid streams flowing from the adjoining 

 mountains, and was distributed by currents along the shore. 



The beaches would appear essentially to have been formed by waves and 

 currents, as there are very few signs of ice action such as are seen around 

 the shores of Lakes Winuipegosis and Manitoba to-day. 



Where most conspicuously developed the beaches are covered, as a rule, 

 with only a meagre growth of short grass, which in some of the more north- 

 ern parts is varied with a few stunted trees of Banksian pine. They thus 

 often form beautiful dry roads through country that would otherwise be an 

 impenetrable forest. 



So far as the eye can detect, the line of the crest of the ridge is quite 

 horizontal, but careful measurements show it to rise gradually and regularly 

 towards the north, just as the crests do in Minnesota and Dakota. At 



