226 A. HAWKS THE EE-rNTEODTJCTIOIf 



they eat bracken, grass, or young shoots growing about the place, 

 or they grub up roots. Their work is all done at night. They 

 are very regular in their habits, usually coming out about seven in 

 the evening, and going home again about seven in the morning. 



By means of the principal dam they have made a large pool at 

 the lower end of the enclosure. We examined this dam carefully ; 

 it is about 70 feet in length. Its greatest height is about 8 feet, 

 and the breadth of its base at the deepest part of the pool, 15 to 

 20 feet. This they have built up piece by piece and year by year, 

 first beginning by damming the little stream, then raising and 

 ■widening the dam, and thus making the pool broader and deeper. 

 It is constructed of wood, grass, and sand, with stones here and 

 there, which have served to keep the other material in place until 

 more was built on it. They carry the material with their mouths 

 and fore-feet. They use their fore-feet like hands, in fact they are 

 formed more like hands than feet, and with them they plaster on 

 the mud and knead it in among the sticks. It was formerly said 

 that they used their tails to plaster the mud smoothly. That, 

 however, is a myth, like that of the kangaroo using his tail for 

 leaping. Of course as the embankment increased in height and 

 width, the pressure of the water against it much increased, and 

 this the builders had taken care to provide for. They built it partly 

 in arched form against the stream, with greater breadth serving as 

 buttresses between the arches, besides which there are props behind. 

 The embankment is not arched throughout, but in those places only 

 where the pressure of the water is greatest. This illustrates what 

 the Rev. J. G. Wood says (quoting I believe from Audubon, to whose 

 work I have not been able to refer) : "When the different parts 

 of the stream run with varying velocity, the formation of the dam 

 is really a triumph of engineering skill, for wherever the stream is 

 gentle the dam is built straight across it, but wherever the current 

 runs smartly the dam is curved, so as to present a convex surface 

 to its force." This is a very neat testimony to the sagacity, the some- 

 thing more than instinct, of the beaver. In one place behind this 

 large dam a tree has been cut, and has fallen towards the dam, so that 

 the severed stem rests against the rooted trunk from which it was 

 cut, and thus the trunk and the stem with its branches are made to 

 serve as a buttress to the dam ; behind this same dam, where it is 

 high, they have laid round pieces of wood horizontally to serve as 

 a ladder. They keep the top of the dam perfectly level, so that 

 the water runs over evenly — a very important matter when flood- 

 water comes down ; but so substantially has this dam been built, 

 that it has sustained no damage to speak of during the seven years 

 it has been standing. 



There are other smaller dams higher up, and in one of these a 

 growing tree was made use of ; the dam was carried across just 

 above it, and about the centre rested against it. The tree was of a 

 kind not used for food by beavers, but they knew or found out that 

 the pressure of the wind on the upper part of the tree would by 

 rocking it about disturb the stability of the dam, so they just cut 



