486 THE POPULAR SCIENCE MONTHLY. 



I am inclined to believe that large areas of our wet woods and the open 

 border-lands along our streams are completely overturned to tlie depth 

 of two feet or more in the course of half a century by the actions of 

 these animals. It is not impossible, indeed, that the very fine division 

 of the soil which characterizes the regions inhabited by these creat- 

 ures may be in good part due to their action. In this manner the 

 creatures may have in part worked to bring about the very conditions 

 which best serve their needs. 



In open grounds, in natural prairies or grass-plains, the smaller 

 species of ants are extremely effective agents in overturning the soils. 

 Wherever the ground remains for some time unplowed it becomes 

 occupied by these creatures. In the sandy soils of Eastern Massa- 

 chusetts, the overturning accomplished by these creatures assumes a 

 geological importance. For many years I have been puzzled by the 

 fact that the glacial terraces and plains of this region were exten- 

 sively covered to the depth of a foot or more by a coating of fine sand 

 and very small pebbles, while below the depth of a foot pebbles of 

 larger size are very numerous, and the spaces between them but im- 

 perfectly occupied with any material. It is obviously impossible to 

 explain these conditions through the action of earth-worms, for the 

 reason that these creatures are rarely found in soils of this description. 

 From much observation I have become convinced that this coating of 

 sandy material is, to a great extent, to be explained by the action of 

 various species of ants in the forest condition by the work of the 

 larger black ants, and in the condition of open plains by that of the 

 smaller species. 



The amount of material which these creatures bring to the surface 

 in a single season is surprising. At several points in Eastern Massa- 

 chusetts I have found the surface to contain at least one ant-hill to 

 each square foot of area, or about forty thousand hills to the acre. 

 This is, probably, an exceptionally great number ; it will, perhaps, be 

 safer to estimate the number at twenty thousand to the acre. The 

 incoherent heaps of excavated matter which these creatures form are 

 quickly washed away by the rain, or in many cases, are blown away 

 by strong winds, and so scattered over the surface. As soon as de- 

 stroyed they are, in most cases, rebuilded, the result being that a single 

 hill is reconstructed at least half a dozen times during a season. I 

 have estimated that the amount of material brought to the surface 

 often exceeds three cubic inches to each square foot of surface in a 

 single year, or about a fiftieth of an inch of the whole area each year. 

 Thus, in the term of fifty years, the accumulation of material on the 

 surface would amount to as much as an inch, and reckoning the soil 

 as having an average depth of one foot, a total overturning would be 

 accomplished in less than a tliousand years. It is likely that in some 

 cases, over considerable areas, a tolerably complete overturning is 

 brought about in less than a quarter of this time. 



