250 WASTE-LAND WANDERINGS. 



out difficulty, and passed through a layer of very com- 

 pact earth. Scores of tortoises do the same every year, 

 and possibly reach greater depths. 



If, then, such excavations without removal to the sur- 

 face of the displaced earth is practicable for a tortoise, 

 may it not be equally so for a chipmunk, that works in 

 far less compact earth and in a horizontal direction? 

 The task is different in the case of the mammal, to be 

 sure, but this difference is less significant than may at 

 first be thought. I refer to preserving the burrow open 

 as it proceeds. I find that in the sandy hill-side, where 

 all the burrows are which I have examined, if you push 

 a stout tube into the earth and remove so much as the 

 tube will contain, then the side of the excavation made 

 will soon crumble; but if a stick of the same size is 

 pushed into the earth, the displaced portion, by being 

 made more compact, is firmly fixed, and the little tunnel 

 is comparatively permanent. Does not the peculiar dig- 

 ging motion of a burrowing mammal have the effect 

 necessarily of compacting the sides of the tunnel as it 

 progresses? The particles detached by the projecting 

 fore-feet must unavoidably fall under the neck and belly 

 of the animal, and the motion of the rapidly moving 

 limbs must pat this material, which again is pressed 

 down by the weight of the animal's abdomen. In such 

 soils as I have examined, all of very loose texture, there 

 did not seem to be any difficulty in rapidly tunnelling, 

 but skill was required in so compacting the sides of the 

 excavation that they would remain intact. 



But what positive evidence have we that a mammal 

 can penetrate even sandy soils and form a tunnel as it 



