286 SCOTTISH GEOGRAPHICAL MAGAZINE. 



Pleistocene geology, such as the elevation and partial subsidence of the 

 continent, with consequent changes in the ocean currents and in the 

 temperatures of both sea and land ; also with the shifting of glacial 

 centres, followed by the presence or absence of ice in certain regions at 

 different times. The distribution of the Banksian pine and the balsam 

 poplar will serve to illustrate the above inference. The former seems 

 to shun proximity to the sea, while the latter seeks it. If we trace 

 the boundary of the Banksian pine throughout its whole course, we shall 

 observe that it nowhere touches the salt water, while the balsam poplar 

 is found everywhere near to the sea as far north as it can grow, but it 

 is apparently wanting over a great area in the central part of Labrador, 

 which is probably too far inland for it to flourish. The southern lobe 

 of this vacant space extends into the Ottawa valley in precisely the same 

 south-westerly direction that was followed by the land ice from the old 

 centre of glaciation in central Labrador to this valley. The erratic 

 course of the balsam poplar line north-west of Hudson Bay may be con- 

 nected with changes which took place in the later movements of the 

 glacier ice in that region. 



CONTINUATION OF PLEISTOCENE CONDITIONS. 



Around the shores of James Bay the land is only moderately elevated 

 for a considerable distance inland, especially on the west side, where a 

 level tract extends for more than 100 miles from the sea. This border 

 of low land affords abundant evidence of having been submerged in post- 

 Pliocene times, and the line of the Banksian pine still skirts its margin 

 all the way round, not having had time as yet to invade the old sea- 

 bottom to any appreciable extent. It will be observed that the southern 

 boundary of the Banksian pine reaches its extreme limit between the 

 lower part of the Ottawa river and Georgian Bay of Lake Huron, where 

 it intersects the 45th parallel. In explanation of this decided southward 

 curve, we find unusually high ground to the north-west of Ottawa and 

 throughout much of the tract between this city and Georgian Bay, which 

 would stand out as a promontory when the sea covered the country to 

 the south and east, as it is known to have done at about the same time as it 

 submerged the district around the head of James Bay. An outlier of 

 the Banksian pine occurs in New Brunswick, and another in Nova Scotia, 

 both being at some distance from the open sea. 



PECULIARITIES or THE WHITE CEDAR LINE. 



The boundary of the white cedar is perhaps the most remarkable tree- 

 line upon the map. In the central part its course is tolerably direct, but 

 in both the east and west it turns southward and crosses the other tree- 

 lines at right angles. If it had followed the average course of the 

 boundaries of the other trees with which it is associated, it would have 

 included the island of Anticosti, the whole of the maritime provinces, 

 and the greater part of Newfoundland, in all of which the conditions of 

 climate, soil, etc., are evidently as favourable for the growth of this tree 

 as they are in New Brunswick and the Gasp6 peninsula, where it is quite 



