PAST AND FUTURE OF BRITISH MAMMALS 287 



this dam they cut down trees and do mischief. But on 

 deep, slow streams, such as the Thames, they make 

 burrows in the bank and c lodges,' but do not attempt 

 to build dams, because the water is deep enough for 

 their wants. All they need is enough willow-bark to 

 feed on. If anyone would turn out a few beavers on 

 the Thames, and let them have the run of an osier-bed, 

 they would probably increase and multiply. 



