68 ANIMAL INTELLIGEJSrCE. 



has acquired his greatest reputation. These dams are 

 built chiefly to maintain the water in the pond at a. fixed 

 level, and that is from one to three feet above the 

 entrance to their "lodges" or "burrows." They are of 

 two kinds — the "stick dam" and the "solid bank 

 dam." The " stick dam " is made of poles and sticks 

 interlaced together, through which the water percolates 

 throughout its entire length. This is of comparatively 

 easy construction and is used in those ponds or streams 

 where the flow is sluggish and the pressure such that a 

 solid earthwork is not required. 



The " solid bank dam " is a much more elaborate and 

 difiicult piece of engineering, and is used when these 

 conditions are reversed. It is made of sticks and brush, 

 cemented with mud and often weighted with stones. A 

 regular opening or trough is made in the top to provide 

 for the overflow. This trough is enlarged or contracted 

 according to the varying amount of water that must be 

 drawn off to keep the pond at the proper level. This 

 dam is a solid structure capable of supporting the weight 

 of a horse, is from two to six feet high and from six to 

 eighteen feet broad at the base, with sloping sides nar- 

 rowing at the top. Some of these dams attain an extra- 

 ordinary length. There is a remarkable one on the 

 tributary of the Esconauba River. The beavers first 

 built a dam across the channel about 20 feet in length. 

 The water backed up, of course, and flowed around to 

 the left. To shut this in the dam was extended about 90 

 feet. The shore end of this abutted against a natural 

 bank, which extended back along the border of the pond 

 for about 1,000 feet, nearly at right angles to the arti- 

 ficial dam, with an occasional break which the beavers 

 filled in. Around the open end of this natural bank the 

 water again overflowed, running down the land side of 

 it and emptying into the outlet at the foot of the dam. 

 This had to be stopped, so another earthwork 420 feet 



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