BEAVER MEADOWS 103 
taken August 17, 1923, shows the pond practically all 
covered with coarse grass. ‘There were still soft muddy 
places here and there, and the channel which can be seen was 
very soft mud, as my assistant discovered when he stepped 
on it and went in above his knees. 
In a case which came under my observation in Colorado 
I found on a small stream a good-sized pond containing a 
lodge. This pond was formed by a dam one hundred and 
thirty feet long. This wasin 1913. The following year the 
dam was broken through at the stream channel, and the 
pond drained, and in 1915 it was overgrown with grass. 
When examining the place in the autumn of 1922 I found 
that the stream channel had been very much deepened, 
presumably by a flood the previous year, and a new dam 
built between the banks, forming a pond over two hundred 
feet long. The old dam, though almost obliterated in 
places, could be traced on either bank above, more than four 
feet higher than the new water level. The old pond was 
now a meadow covered with grass and the old lodge a ruin 
(Figs. 51 and 52). 
The character of the material with which a beaver pond 
may be filled is variable. Sometimes it is a fine silt which 
makes an excellent soil, and probably this is the first material 
to be deposited. On the other hand I saw some ponds in 
the Yellowstone which were being filled, or were already 
filled, with a coarse gravel. At Longs Peak Inn, Colorado, 
the site of an old beaver pond was excavated to make an 
artificial pond, and here I found a fine gravel or coarse 
sand resulting from the grinding up or disintegrating of the 
granite country rock. ‘This seemed to be devoid of humus 
or vegetable matter which might serve as plant food. On 
top of this, however, there appeared to be a layer of black 
mould in which grass and willows grew. 
Many beaver meadows become covered with a dense 
growth of willows, almost impenetrable at times (Fig. 53). 
