248 STRANGE DWELLINGS 



ing 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 water 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 completely 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, 

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

 through which the river passes, and is covered with fertile 

 alluvium. 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. Origi- 

 nally, the dam is seldom more than a yard in width where it 

 overtops the water, but these unintentional additions cause a 

 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 further 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 hungiy, they dive to their hidden stores, pull out a few 

 branches, carry them on land, nibble away the bark, and drop 

 tne 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 

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



