42 THE ROYAL SOCIETY OF CANADA 



conditions necessary for the formation of such bogs in other countries 

 were also necessary for the formation of these "muck" deposits. 



Sphagnum and Hypnum bogs form on wet land, preferably where 

 the soil is impervious, and where the surface is so level that the water 

 will not run off, or on gently sloping land which is kept wet by a 

 perennial supply of spring water flowing over a hard clay bottom. 

 Such bogs occur in many parts of Great Britain and Ireland and 

 throughout all the temperate and well watered parts of North America. 

 In the Klondike district, where they also occur, the conditions would 

 appear at first sight to differ somewhat from those prevailing farther 

 south. Many of the bogs and beds of "muck" occur on low benches, 

 and alluvial bottom lands of the valleys, overlying beds of gravel. 

 If the country were enjoying a temperate climate, those gravel beds 

 would be well drained and would be so dry that they would certainly 

 support only a scanty vegetation. The question at once arises as to 

 why this swamp vegetation ever grew on these gravels, and how 

 it attained so great a thickness. 



It would appear that the primary condition necessary for the for- 

 mation of such bogs was that the gravel flats on which they were to 

 grow should be permanently wet, and the only agency that would seem 

 to me competent to cause them to be impervious to water at all times, 

 and permanently wet throughout the growing season of the summer, 

 would be frost. If they had not been frozen they would certainly have 

 been drained and dry during the summer season. It is probable, there- 

 fore, that these gravel flats had been permanently frozen during a pe- 

 riod of great cold at the beginning of an early Glacial Epoch before bog 

 mosses began to grow on them, and it is also probable that at this 

 time the mean annual temperature of that country was considerably 

 lower than it is at present. Bare uncovered gravels will not freeze 

 permanently at the present time in the Klondike, for though they will 

 now freeze to a considerable depth every winter they will thaw out 

 again during the following summer. Let us consider, then, that a 

 period of great cold set in and that the water included in the lower 

 parts of the gravel was kept frozen throughout the summer. In this 

 way a bottom impervious to water would be formed and wherever 

 there was a supply of surface water bog mosses would begin to grow. 

 At a later date spruces and willows would take root on the beds of 

 moss, just as they do at the present da}^ 



In the epoch preceding the Glacial Period, when the underlying 

 and adjoining ground was not frozen, the streams, when in flood, eroded 

 their banks, washed down gravel and spread it out over other parts of 

 the bottom land. But with the advent of the period of great cold the 

 ground, as we have shown, became permanently frozen, and in con- 



