1640 THE STORY OF THE UNIVERSE 



all constant, not at the mercy of the rise and fall of 

 the stream. A sudden and excessive flood is the one 

 danger likely to prove fatal to these dikes; but even 

 our own constructions are threatened under such 

 circumstances. 



When the beavers, tempted by abundance of 

 willows and poplars, of which they eat the bark and 

 utilize the wood in construction, have chosen a site, 

 and have decided to establish a village on the edge of 

 the water, there are several labors to be successively 

 accomplished. Their first desire is to be in possession 

 of a large number of felled trunks of trees. To ob- 

 tain them they scatter themselves in the forest bor- 

 dering the stream and attack saplings of from twenty 

 to thirty centimetres in diameter. They are equipped 

 for this purpose. With their powerful incisors, 

 worked by strong jaws, they can soon gnaw through 

 a tree of this size. But they are capable of attack- 

 ing trees even more than 100 cm. in diameter 

 and some forty metres in height with great skill 

 and adaptability; "no better work could be accom- 

 plished by a most highly finished steel cutting tool, 

 wielded by a muscular human arm" (Martin) . They 

 operate seated on their hindquarters, and they make 

 their incision in the wood with a feather edge. It 

 was once supposed that they always take care so to 

 direct their wood-cutting task that the tree may fall 

 on the water-side, but this is by no means the case, 

 and appears to be simply due, as Martin points out, 

 to the fact that trees by the water-side usually slope 

 toward the water. The austerity of labor alter- 

 nates, it may be added, with the pleasures of the 



