Page:Popular Science Monthly Volume 34.djvu/49

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HABITS OF THE GREAT SOUTHERN TORTOISE.

begin the burrow, they endeavor at once to penetrate downward to the level in which they obtain their food. At the outset they manage, by frequently backing out of the passage, and thrusting the earth behind them in their retreat, to clear a considerable opening. When they have advanced a few feet in the excavation, they cease to discharge the material excavated in their advance, but thrust it behind them, and leave it lying in the chamber, which it entirely closes. With this storage-room provided, the gophers are able to advance through the earth for the distance of some yards; but as the earth compacted by its own weight, by the pressure exercised through the expansion of roots, and the action of the rain, occupies less space than the same material loosened in the progress of the burrow, they soon become hampered in their movements. They then turn toward the surface and continue the excavation upward until they have attained very nearly to the open air. They then use the great strength which they clearly possess to thrust a quantity of the burrowed material upward until it rises above the surface in the form of a cone, and by the space in the burrow thereby gained they are able to go a few feet further in their tortuous line of advance, when they must again seek to discharge a portion of the earth in the manner just described. So the creature proceeds in its devious underground way, coming near the surface and pushing out a portion of the sand at intervals of from two to five feet in its path. In this manner it appears to journey at times for a distance of hundreds of feet before it again has occasion to come to the open air.

For the greater portion of its journey, the path of this creature seems to lie within two or three feet of the surface, that being the level in which it finds the roots which afford it food. It appears, however, from the points at which they emerge in the railway-cuts, not unlikely that they occasionally penetrate to the depth of six feet below the top of the soil. Although they plentifully occur throughout a region having a superficial area of nearly one hundred thousand square miles, they appear to exercise a considerable choice as to the ground they inhabit. They demand, in the first place, that the water-level shall not be within a dozen feet of the surface, and that the material they traverse shall be a very open-textured sand. This is probably because in the rainy season any considerable rise in the level of the groundwater would be destructive to them; unless they could quickly escape from their burrows, they would be drowned. It is often possible, through this habit, to determine in an approximate way the depth of the Tertiary beds of clay and other indurated materials which at many points lie near the top of the sand which envelop the surface in the Southern States. Where these beds,