But after he has progressed inwards a few feet, the vizcacha is
no longer satisfied with merely scattering away the loose earth he
fetches up, but cleans it away so far in a straight line from the
entrance, and scratches so much on this line (apparently to make the
slope gentler), that he soon forms a trench a foot or more in depth, and
often three or four feet in length. Its use is, as I have inferred, to
facilitate the conveying of the loose earth as far as possible from the
entrance of the burrow. But after a while the animal is unwilling that
it should accumulate even at the end of this long passage; he therefore
proceeds to make two additional trenches, that form an acute, sometimes
a right angle, converging into the first, so that when the whole is
completed it takes the form of a capital Y.
These trenches are continually deepened and lengthened as the burrow
progresses, the angular segment of earth between them, scratched away,
until by degrees it has been entirely conveyed off, and in its place is
the one deep great unsymmetrical mouth I have already described. There
are soils that will not admit of the animals working in this manner.
Where there are large cakes of "tosca" near the surface, as in many
localities on the southern pampas, the vizcacha makes its burrow as best
he can, and without the regular trenches. In earths that crumble much,
sand or gravel, he also works under great disadvantages.
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