Canadian Agriculture. 
227 
be dried and blown away by the wind. At tlic same time their subterranean 
passages serve to drain off tlio superficial water and to injure the stability of 
the surface of the ground above them. In Britain the mole and rabbit are 
familiar examples. In North America the prairie dog and gopher have 
undermined extensive tracts of pasture land in the west." * 
These last are little animals allied to the squirrel, the so-called 
prairie dog being a rodent, and not a carnivore. I saw numbers 
of them scampering along the ground beside the track of the 
Canadian Pacific Railway. Their open burrows are incon- 
venient to horses travelling across the prairie, and sometimes 
the animals become a nuisance by devouring newly sown seed ; 
on the Bell Farm a halfpenny each is given for their tails. 
The beaver, again, though receding at the approach of man, 
has left unmistakable signs of his former presence : — ] 
" The flow of streams is sometimes interfered with, or even diverted, by the 
operations of animals. Thus the beaver, by cutting down trees (sometimes 
one foot or more in diameter) and constructing dams with the stems and 
branches, checks the flow of water-courses, intercepts floating materials, and 
sometimes even diverts the water into new cliannels. Tliis action is typically 
displayed in Canada and in the Kocky Mountain regions of the United States. 
Thousands of acres in many valleys have been converted into lakes, which, 
intercepting the sediment carried down by the streams, and being likewise 
invaded by marshy vegetation, have subsequently become morass and finally 
meadow-hand. Tlie extent to which, in these regions, the alluvial formations 
of valleys have been modified and extended by tlie operations of the beaver is 
almost incredible." \ 
The conservative action of animals upon the earth's surface is 
less marked, but the following case deserves mention : — • 
"In the prairie regions of Wyoming and other tracts of North America, 
some interesting minor effects are referable to the herds of roving animal.-i 
which migrate over these territories. The trails made by the bison, the elk, 
and the big-horn or mountain sheep, arc firmly trodden tracks on which vege- 
tation will not grow for many years. All over the regioa traversed by the 
bison, numerous circular patches of grass are to be seen which have been 
formed on the hollows where this animal has wallowed. Originally they are 
-shallow depressions formed in great numbers where a herd of bisons has rested 
for a time. On the advent of the rains they become pools of water ; thereafter 
grasses spring up luxuriantly, and so bind the soil together that these grassy 
patches, or ' bison-wallows,' may actually become slightly raised above the 
■general level if the surrounding country becomes parched and degraded 
by winds." % 
On the level prairies the buffalo trails may be seen, stretching 
away in dark and well-defined straight lines, till the eye fails 
to distinguish them in the distance. 
* 'Text-book of Geology,' p. 455. Ihid. 
X Ihkl. ; and Comstock in Captain Jones's ' Keconnaissance of N.W. Wvomin";,' 
1875,, p. 175, 
Q 2 
