456 Life-histories of Northern Animals 



Hofer took the 3 Beavers sent to the National Zoo, and as 

 nearly as we knew there were 4 more left in the pond. After 

 spending two days with compass and measuring rod I pro- 

 duced the accompanying plans ^^ of the Beaver's system of 

 interior navigation (Fig. 129). The source of all the water 

 was a spring or springs in the marsh above. This resulted in 

 a tiny rill about 18 inches wide and averaging 3 inches deep 

 across, and yet was so managed by this industrious family as 

 to result in 13 ponds, the largest of which is 6 or 7 feet 

 deep, 250 yards long, 80 yards wide, and covering about 3 

 acres. 



This is made by the great or central dam, which is doubt- 

 less the oldest; for the aspens opposite were evidently the first 

 to be cut away, the willows in the pond it makes are dead, the 

 house is in its pond, and, finally, the fact of its superior size 

 is some guarantee of its seniority. This dam is built largely 

 of stone where it reaches the talus of the cliff, and entirely of 

 mud and sticks where it runs into the marsh. During the first 

 night of my visit the Beavers added a charred pole, 18 feet long 

 and 5 inches thick — the only pole I saw used there. This 

 dam is 301 feet long, 15 feet wide at base, 4 J feet high in the 

 deepest place, measured to the bed of the stream just below 

 the face; it contains between 100 and 200 tons of material. 

 Such a structure must have taken years of labour and genera- 

 tions of Beavers to produce. Twenty-four yards below this 

 is the second dam, most happily, if unwittingly, placed to 

 relieve the pressure on the first. 



Morgan describes" in detail dams which were 488 feet 

 and 551 feet long. 



The highest dam he had knowledge of is "about ^^ 

 feet long, 12 feet in vertical height, and with a slope of inter- 

 laced poles on its lower face upward of 20 feet in length." ^* 



The largest dam, that is, the one which he is ''well assured 

 is not surpassed in magnitude by any other Beaver dam in 

 North America," " is 260 feet 10 inches long, 6 feet 2 inches 



"These I published in Recreation Mag., October, 1897, pp. 286-9. 



"Am. Beaver, pp. 129 and 122. ^* Ibid., p. 119. ^^ Ibid., pp. 99 and 97. 



