run seepage water into it, and also to act as a wall 

 across the canal to hold the water. The most 

 southerly sixty feet of this canal on the edge of the 

 foothills ran uphill, and was about four feet deep 

 at the upper end, four feet higher than the end by 

 the house. The dam across it was supplemented 

 by a wall forty-eight feet further on. This wall 

 was simply a short dam across the canal, in a 

 part that was inclined, and plainly for the purpose 

 of retaining water in the canal. The upper part 

 of the canal was filled with water by a streamlet 

 from off the slope. Apparently this canal was 

 old, for there was growing on its banks near the 

 house, a spruce tree, four inches in diameter, that 

 had grown since the canal was made. 



The wall or small dam which beaver build 

 across canals that are inclined represents an in- 

 teresting phase of beaver development. That 

 these walls are built for the purpose of retaining 

 water in the canal appears certain. They are 

 most numerous in canals of steepest incline, 

 though rarely less than twenty feet apart. I have 

 not seen a wall in an almost dead-level canal, ex- 

 cept it was there for the purpose of raising the 



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