274 GEOGRAPHICAL DISTRIBUTION OF PLANTS. 



man's height in the alluvial deposits, and are varied also by 

 other shrubs that have been noticed in the descriptions in- 

 terspersed through the preceding pages. These are merely 

 the foreground incidents, however ; the sombre spruce 

 everywhere forms the back ground. 



The agency of man is working a change in the aspect of 

 the forest even in the thinly peopled north. The woods 

 are wasted by extensive fires, kindled accidentally or in- 

 tentionally, which spread with rapidity over a wide extent 

 of country, and continue to burn until they are extin- 

 guished by heavy rains. These conflagrations consume 

 even the soil of the drier tracts ; and the bare and whitened 

 rocks testify for centuries to the havoc that has been made. 

 A new growth of timber, however, sooner or later springs 

 up ; and the soil, when not wholly consumed, being gene- 

 rally saturated with alkali, gives birth to a thicket of 

 aspens instead of the aboriginal spruce. 



The frozen subsoil of the northern portions of the wood- 

 land country does not prevent the timber from attaining a 

 good size, for the roots of the white spruce spread over the 

 icy substratum as they would over smooth rock. As may be 

 expected, however, the growth of trees is slow in the high 

 latitudes. On the borders of Great Bear Lake, four hun- 

 dred years are required to bring the stem of the white 

 spruce to the thickness of a man's waist. When the tree 

 is exposed to high winds, the fibres of the wood are spi- 

 rally twisted; but in sheltered places, or in the midst 

 of the forest, the grain is straight, and the wood splits 

 freely. 



At the limit of the woods the white spruce is everywhere 

 the most advanced tree, growing either solitarily, with its 

 branches clinging to the ground and its dwarfed top bent 

 from the blast, or in small clumps in some favourable 

 locality. The Salix speciosa may indeed be said to pass 



