Vegetation of Northern Cape Breton. 347 



impossible. This latter point is well illustrated by conditions 

 near an old settlement along Indian Brook, which has been 

 deserted for many years. The climax forest was cut over in 

 two adjoining tracts, one of which was afterward burned over, 

 the other not. To-day, perhaps forty years after cutting, the 

 unburned area is covered by a forest of yellow birch, sugar 

 maple, and other climax trees, with scattered specimens of paper 

 birch and large-toothed aspen {Poptihis grandidentata) . The 

 burned area, on the other hand, supports an almost pure forest 

 of paper birch. In both forests the balsam fir is the most 

 conspicuous undertree. 



C. Primary Formations of the Hydrarch Series 

 I. The Formation-types of Lakes and Ponds Inland 



a. INTRODUCTORY 



The ecological relationship of lakes and szvamps. — For pur- 

 poses of convenience, lakes and swamps are here treated under 

 separate headings, but, broadly speaking, they belong to the 

 same family and there is no sharp dividing line between them. 

 Through the activity of various agencies a lake or pond may 

 become filled in and converted into a swamp. The manner in 

 which this transformation may be accomplished by plants, 

 together with the changes in vegetation which accompany the pro- 

 cess, is outlined in the following paragraphs, quoted, with slight 

 alterations, from an earlier paper by the writer ('15, pp. 

 175-178) : 



The important role commonly played by plants in the conversion of 

 lakes into swamps has long been recognized. When the plants in a lake 

 die, their remains sink to the bottom where, because of insufficient 

 oxidation, the vegetable debris is only partially decomposed. In this way 

 there collects on the floor of the lake a layer of vegetable muck, or peat; 

 and through the continued addition of fresh layers the deposit is gradu- 

 ally thickened and built upward. This constructive process may go on 

 until ultimately the surface of the deposit reaches the level of the water, 

 when the lake gives way to a swamp. But the rate at which the sub- 

 stratum is built up and the length of time which elapses before it reaches 

 the water level varies greatly in dififerent parts of a lake. Plants grow 

 most luxuriantly in shallow water ; they may be practically absent from 

 the deeper areas. It follows, therefore, that the accumulation of muck 

 or peat proceeds much more rapidly in shallow than in deep water — so 



