"378 ANIMAL INTELLIGENCE 



Of no apparent use for beaver occupation, but yet subserving 

 the impoi-tant purpose of setting back water to the depth 



of twelve or fifteen inches ; and the small dam, by 



maintaining the water a foot deep below the great dam, 

 diminishes to this extent the difference in level above and 

 below, and neutralises to the same extent the pressure of the 

 water in the pond above against the main structure. 



* Whether,' adds Mr. Morgan, with commendable caution, 

 ■* the lower dam was constructed with this motive and 

 for this object, or is explainable on some other hypothesis, 

 I shall not venture an opinion.' But as, he further adds, 



* I have also found the same precise work repeated below 

 other large dams,' we are led to conclude that their corre- 

 lation cannot at least be accidental ; and as it is of so 

 definite a character, there really seems no 'other hypothesis' 

 open to us than that of its having reference to the sta- 

 bility of the main dam. Yet, if this is the case, it be- 

 comes in my opinion simply impossible to attribute the 

 fact to the operation of pure instinct. 



Again, Mr. Morgan observed one case in which, higher 

 up stream than the main dam, there was constructed 

 another dam, ninety-three feet long, and two and a half 

 feet high at the centre : — 



A dam at this point is apparently of no conceivable 

 use to improve the lake for beaver occupation. It has one 

 feature, also, in which it differs from other dams except those 

 upon lake outlets, and that consists in its elevation, at all 

 points, of about two feet above the level of the lake at ordinary 

 stages of the water. In all other dams, except those upon lake 

 outlets, and in most of the latter, the water stands quite near 

 their crests, while in the one under consideration it stood 

 about two feet below it. This fact suggests at least the inference, 

 although it may have but little of probability to sustain it, 

 that it was constructed with special reference to sudden rises 

 of the lake in times of freshet, and that it was designed to hold 

 this surplus water until it could be gradually discharged through 

 the dam into the great space below. It would at least subserve 

 this purpose very efficiently, and thus protect the dam below it 

 from the effects of freshets. To ascribe the origin of this dam 

 to such motives of intelligence is to invest this animal with a 

 higher degree of sagacity than we have probable reason to 



