40 THE POPULAR SCIENCE MONTHLY. 



too compact for the uses of this creature, come within a short dis- 

 tance of the surface, they avoid the ground. 



The geological effects of this creature in the district which it 

 inhabits are considerable. In a region extensively occupied by 

 them, they turn over the earth, to the depth of some feet, with 

 amazing rapidity. On selected areas chosen to represent the work 

 done by these animals I found that the number of hillocks varied 

 from fifty to two hundred to the acre, and that the heaps con- 

 tained an average of rather more than one fourth of a cubic foot 

 of sand when reduced to the measure of compactness which it oc- 

 cupied when in its original place. I came to the conclusion 

 that it would be safe to estimate that in each year this soil matter 

 thrown up by the gophers on the surface of an acre amounted to 

 an average of fifty cubic feet, the greater portion of which was 

 uplifted from a depth of a foot or more below the surface. At 

 this rate they would completely overturn the soil, for the depth of 

 a foot or more, in about eight hundred years. In addition to the 

 effect produced by the process of throwing out the earth upon the 

 surface, these creatures accomplish a vastly greater amount of 

 subsoiling by continually ascending and descending in the earth, 

 pushing the earth behind them as they go. I am inclined to think 

 that they displace vertically, about the amount of a foot or more, 

 all the sands to the depth of about three feet in the course of less 

 than a century. The result is, that in the regions they occuj^y 

 there is no distinct soil coating whatsoever ; the thin layer of half- 

 decayed vegetable matter, rarely exceeding an inch or two in 

 thickness, lies immediately upon the sands, which are scarcely 

 commingled with the humus material. Although the rapid decay 

 of vegetation in the warm climate of the South may in part ac- 

 count for this peculiarity, I think that it in the main is due to the 

 action of these creatures. This view is supported by the observa- 

 tion as to the character of the soil in places where the gophers 

 have not done their underground work. Thus, where the ground 

 is too wet for their occupancy, we commonly find a thick coating 

 of vegetable matter and a soil which is charged with humus to a 

 considerable distance from the surface. The wet " hammock " or 

 " hummock " lands, which exist as occasional patches in the sandy 

 districts where these animals are plenty, apparently owe in good 

 part their more normal character of soil to the exemption from 

 the overturning of the superficial materials which these creatures 

 effect. 



There is another important way in which these gophers have 

 influenced the geological conditions of the districts they inhabit. 

 The sands through which they make their burrows have evidently 

 been deposited by water-action. They were probably originally 

 in the stratified form, but so thoroughly have they been overturned 



