Yellowstone Beaver 211 



way across the river (figure 59). One of these was on one side, 

 the other two on the other, and they were placed in such a manner 

 as to deflect the water first to one side, then back again, forming 

 deep, quiet pools. The diversion dam on Carnelian Creek, already 

 described (p. 196), also illustrates this method of building (figure 

 60). 



As to the length of dams, they vary from a foot or two up to 

 several hundred feet in length. The longest I measured was 35c 

 feet long, on the North Fork of Elk Creek (figure 40). Seton 

 speaks of one near Obsidian Cliff which he thought was 400 yards 

 long. Enos Mills mentions one near Three Forks, Montana, 2,140 

 feet long, mostly old, more than one-half of which was less than 6 

 feet high, two short sections being 23 feet wide at the base, 5 at 

 the top and 14 high. Dams vary in height as in length, but I think 

 they are rarely more than 6 feet high on the lower face, usually 

 less. The thickness of the base varies firstly with the height, and 

 secondly with the age of the dam, for as the material settles with 

 age it tends to spread; and silt also settles at the base, so that even 

 if the structure does not increase in height it may become wider. 



If a dam is abandoned it gradually goes to ruin, yet many of the 

 dams in Yellowstone Park and elsewhere have probably been aban- 

 doned at times for a number of years, and then repaired and reoc- 

 cupied by a new colony of beavers. 



Lodges. Lodges may be divided into two sorts, those built out 

 in the water away from shore, and bank lodges. The former must 

 have a foundation of some sort to start with, as a small island, or 

 an elevation of the pond bottom sufficient for a beginning. Seem- 

 ingly the lodge begins with a burrow, covered with mud and sod, on 

 which sticks are laid, much as in building a dam. The interior is 

 kept hollowed out as the work progresses, and the structure is more 

 loosely built above the chamber to permit of ventilation. The floor 

 is a few inches above water level, and is furnished with a bed of 

 grass or shredded wood fiber. Dugmore says there are two levels 

 to the floor, the lower for drying and feeding, the upper for a bed. 

 There are usually at least two entrances to a house. In size they 

 range from 8 feet to 10 feet in diameter and up. The largest house 

 I have ever seen and measured is one in the large pond on Tower 

 Creek previously mentioned (figure 61). It is 21 by 24 feet in 

 diameter, and 7 feet 3 inches above the water level. Five 

 entrances were found. Du«rnore mentions a house in Newfoundland 



