436 HOMES WITHOUT HANDS. 



The dam is formed, not by forcing the ends of the logs into the 

 bed of the river, but by laying them horizontally, and covering 

 them with stones and earth until they can resist the force of the 

 water. Vast numbers of logs are thus laid, and as fast as the wa- 

 ter rises, fresh materials are added, being obtained mostly from 

 the trunks and branches of trees which have been stripped of 

 their bark by the Beavers. 



The reader will remember that many persons have thought 

 that the dam of the Beaver is only an accidental agglomeration 

 of loose logs and branches, without any engineering skill on the 

 part of the animals. There is some truth in this statement, 

 though the assertion is too sweeping ; for, after the Beavers have 

 completed their dam, it obstructs the course of the stream so com- 

 pletely that it intercepts all large floating objects, and every log 

 or branch that may happen to be thrown into the river is arrested 

 by the dam, and aids in increasing its dimensions. 



Mud and earth are also continually added by the Beavers, so 

 that in process of time the dam becomes as firm as the land 

 through which the river passes, and is covered with fertile allu- 

 vium. Seeds soon make their way to the congenial soil, and in 

 a dam of long standing forest trees have been known to grow, 

 their roots adding to the general stability by binding together the 

 materials. It is well known that the fertile islands formed on 

 coral reefs are stocked in a similar manner. Originally the dam 

 is seldom more than a yard in width where it overtops the water, 

 but these unintentional additions cause 0, continual increase. 



The bark with which the logs were originally covered is not 

 all eaten by the animals, but stripped away, and the greater part 

 hidden under water, to serve for food in the winter time. A 

 farther winter provision is also made by taking the smaller 

 branches, diving with them to the foundations of the dam, and 

 carefully fastening them among the logs. When the Beavers are 

 hungry, they dive to their hidden stores, pull out a few branches, 

 carry them on larid, nibble away the bark, and drop the stripped 

 logs on the water, where they are soon absorbed by the dam. 



We have now seen how the Beavers keep the water to the re- 

 quired level, and we must next see how they make use of it. The 

 Beaver is essentially an aquatic mammal, never walking when it 

 can swim, and seldom appearing quite at its ease upon dry land. 

 It therefore n»akes its houses close to the water, and communi- 

 cating with it by means of subterranean passages, one entrance of 



