POCKET GOPHEBS 141 



160 carloads of 50 tons each. "We estimate further that this great quantity 

 of earth is lifted by the gophers an average distance of at least 8 inches; 

 5500 foot tons of energy is expended in excavation alone by these animals 

 in Yosemite Park during a single year! 



The question then presents itself, what are the general effects of all 

 this work upon the terrane at large, upon the vegetation, and even upon 

 the other animal life of the region. Some of these relations borne by pocket 

 gophers to their environment may be enumerated as follows: 



(1) The weathering of the substratum is hastened by the burrow 

 systems carrying the water and contained solvents as well as air to the 

 sub-soil particles and rock masses below. 



(2) The sub-soil is further comminuted and brought to the surface 

 where it is exposed to increased rate of weathering. 



(3) The loose earth brought up and piled on the surface of the ground 

 thereby becomes available for transportation by water; rain and melted 

 snow carry it from the slopes down to fill up glacial depressions and make 

 meadows of them, and when these are full the sediment is carried on still 

 farther by the gathering streams to contribute to the upbuilding of the 

 great and fertile valleys beyond the foothills. 



(4) Water is conserved for the reason that snow melts more slowly 

 on porous ground than on hard-packed soil or bare rock so that the spring 

 run-off is retarded and the supply to the streams below is distributed over 

 a longer period of time; furthermore, the porous soil retains the water 

 longer than packed ground and gives it up with corresponding slowness. 

 Spring floods are less liable to occur, and a more regular water supply is 

 insured to the lowlands. 



(5) A porous, moist soil produces a fuller vegetational cover — forest, 

 brushland, and meadow — and this again favors water conservation. 



(6) The ground is rendered more fertile through the loosening of the 

 soil as well as through its permeation by the tunnels themselves, as thereby 

 both air and water are admitted to the roots of the plants; the mineral 

 constituents of the soil become more readily available, and the rootlets are 

 better able to penetrate the earth. 



(7) The accumulated vegetational debris on the surface of the ground 

 is eventually buried by the soil brought from below by the gophers, and 

 becomes incorporated to form the humus content so necessary for the 

 successful growth of most plants. 



Our readers will have been reminded by a portion of the above con- 

 siderations of Darwin's classical study on the relation of earthworms to 

 soil formation. There is undoubtedly a parallel here, the more significant 

 in that the earthworm is a relatively rare animal in the Sierra Nevada, and 

 what there are of him, are of small size, and of relative inconsequence in 



