I20 The Ottawa Naturalist. [August 



north-east which also is shown in the beaches around Hudson Bay 

 at heights up to 500 feet above sea. 



As the level of the lake fell, the present lake basins became 

 defined and reached their present dimensions. Examples of 

 beaches at different stages might be cited but they are very nume- 

 rous in the western part of the basin along the base of the Pembina 

 and Riding mountains. An example of a former island in the 

 lake at a low stage is to be seen at Stony Mountain where the 

 crest of the hill is crowned by good types of lake beaches. 



The effect on the value of the farming lands of the valley ot 

 this former lake is of great moment. The general boulder-clay 

 covering, which the northern part of the continent has received 

 produces some fine farming land but when this material has been 

 sifted and all its finer constituents spread out over a particular 

 area none but the finest land is to be expected in that area. That 

 the great lake received an enormous amount of sediment especially 

 from the west is evident not only in the soil of the valley itself but 

 in the great valleys worn down through the clay rocks of the 

 plateau. An especially thick deposit would be expected at the 

 mouths of all these streams and particularlj' of the delta in front 

 of the mouth of the Assiniboine which at one time carried the 

 water of the Saskatchewan river while the latter was ice-dammed 

 at the north. The Pembina river as before noted was at one time a 

 great stream, the outlet of a temporary lake, and brought down a 

 heavy deposit. Farther north, the Valley river spread a sediment 

 over the Dauphin country, while the Swan river helped to fertilize 

 the country north-west of Lake Winnipegosis. Beyond the con- 

 fines of Manitoba the Great Saskatchewan spread an immense 

 delta deposit over the low country to the west of Cedar lake but 

 the vast amount of sediment still being catried by this stream, as 

 in the case of the Mississippi, causes its bed to be gradually built 

 up above the surrounding country. Great stretches are therefore 

 available in that region as yet as grazing or hay land only during 

 low water. 



We have thus some clue to the reasons for the fertility of 

 most ol the Red River valley. Other parts that have not been 

 specially fertilized in this way are covered by the ordinary boulder- 

 clay which when disintegrated forms good though heavy soil of 

 fair quality. 



The eastern and northern parts are at present well wooded as 

 well as the summits and slopes of Riding mountain and thence 

 northward. The south and western parts west of Red river are 

 generally open prairie though the true forest is bordered by a more 

 or less wide belt oi' partly wooded country. 



