The North American Forest 15 



gradually became milder, the edge of the conti- 

 nental ice sheet slowly melted, forming immense 

 rivers and lakes. As the land was laid bare, vege- 

 tation recovered the lost territory step by step. At 

 first, the character of the land recently left by the 

 ice was undoubtedly very much like what we find 

 to-day in the Barren Grounds, the solitary regions 

 in the northern part of the British dominions. 

 There we find vast areas covered principally with 

 mosses belonging to the genus Sphagnum, inter- 

 spersed with a few sedges and numerous spe- 

 cies of the heath family. It is a vegetation very 

 similar to that of the peat bogs found occasionally 

 in the Northern States. These moss prairies or 

 tundras were gradually supplanted by the advance- 

 guard of the forest : spruces and poplars, that 

 came slowly marching up from the south and are, 

 in all probability, continuing their advance to this 

 day. These most arctic of American trees were 

 followed by the pines, and these again by the 

 more southern species of hardwood, maples, oak, 

 beeches, and the like. While thus the forest as a 

 whole was advancing northward, the various spe- 

 cies fought among themselves for each locality. 

 This fight continues to the present day, and is 

 changing the distribution of species from century 

 to century. It is very probable, for instance, that 

 both north and south the hardwoods are gaining 

 ground at the expense of the pines and spruces. 

 The hemlock does not reproduce itself in a portion 

 of Wisconsin, and therefore will die out there 



