THE BEAVERS OF NORTH AMERICA 43 



August. Then they see what is the minimum 

 supply of water, and the dam may be built with the 

 least possible trouble. When they finally settle 

 on the exact site, the first sticks are laid, and these 

 in most cases are freshly cut and not peeled. 

 Alders are perhaps the most frequently used, as 

 they are found growing along the waterways and are 

 therefore easily obtained, while their weight allows 

 of their being sunk without much difficulty, and 

 their irregular form of growth helps them to hold 

 on the bottom against the current of water. How 

 quickly a dam is built depends entirely on the 

 urgency of the situation. If it is late in the year, 

 the building proceeds with incredible speed, little 

 more than a week of steady work on the part of a 

 family will see a thirty or forty-foot dam raised to a 

 height of two feet or more. As soon as it backs 

 up the water, the house is commenced and we find 

 that all the different tasks are being attended to 

 simultaneously dams, both main and subsidiary, 

 lodges, tree-cutting, and storing of winter food. 

 Within a few weeks the colony becomes established 

 and the face of the land is changed by the work of 

 these small animals. Larger and larger the pond 

 grows, as the dam is extended, while the banks 

 are covered with fresh, white stumps of fallen 

 trees, as though a gang of lumber-men were at 

 work. Each night sees marked changes resulting 

 from the untiring work of these builders and tree- 

 cutters. If the colony is successful and the site 



