Ei^FBCT or PLANT AND ANIMAL LIFE 383 



process goes on nnceasingly there is always an abundance of new 

 material at the surface each succeeding spring. This heaving 

 action of the frost is abundantly exemplified in these clay regions 

 by the throwing out of fence posts and roots of leguminous plants 

 like clover. In wet boggy lands the heaving action of frost, as 

 exerted on partially buried boulders of small size, is sometimes 

 exemplified in a peculiarly striking manner. The surface of 

 the ground will be dotted here and there with small hummocks, 

 each with a comparatively large crater-like opening at the top. 

 Investigation reveals the fact that at a distance of but a few 

 inches at most below the surface of this crater-like opening is 

 a rounded boulder. The heaving action of the frost forces the 

 boulder gradually upward, causing the turf to first rise with 

 smooth rounded outline, till, through continual pressure from 

 the boulder, it bursts at the top. When the frost leaves the 

 ground, the boulder drops back a short distance, but enough 

 to be quite out of sight, leaving the cavity at the top filled 

 with mud, and looking — in outline — like a small mud volcano. 

 So far as the writers observations go, the heaving action rarely 

 progresses, in these areas, to the point of actually throwing 

 the boulder out upon the surface. Each summer the growing 

 turf makes an attempt at healing the wound, but each winter's 

 frost opens it once more, the alternating forces so nearly bal- 

 ancing that little is accomplished after this pseudo-volcanic 

 stage is reached. 



Insects like the boring bee, the burying beetle, or larger bur- 

 rowing animals, like the ^'woodchuck" of the Eastern states, 

 the prairie dogs, badgers, and spermophiles of the West, exert 

 powerful though local influences in admixing the lower with the 

 upper portions of the soil, and through allowing perhaps a more 

 ready passage of water facilitating oxidation and decomposition 

 at greater depths. (Fig. 2, PL 20.) 



While the effect of these animals may be comparatively in- 

 conspicuous in the regions east of the Mississippi, in portions of 

 the drier regions of the West the surface is so undermined 

 by burrows as to make traveling on horseback at more than a 

 very moderate pace a matter of grave difficulty. W. P. Blake, 

 in the early reports of the Pacific Eailroad Survey, stated that 

 the fine, silty soil of the Tulare valley in California is so under- 

 mined that it is almost impossible to travel over it. '* Mules often 



