THE GRAY GOPHERS 123 
Canada, there are no earthworms to act as pre- 
historic cultivators. The black loam there is 
from one to two feet thick, and is a thoroughly 
mixed soil of both mineral and vegetable par- 
ticles. There is no doubt that, in the absence 
of earth worms, this mixing is done by burrow- 
ing animals, by far the most important of which 
is our subject. In his great work, Life His- 
tories of the Northern Animals, Seton shows by 
text and drawings what an astonishing number 
of active gophers there are (or were) over 
every square mile of that and other regions; 
and the still more astonishing bulk of soil 
brought to the surface from deep layers day 
by day. He cites a district in California with 
an estimated average of 6,000 hills to the acre, 
and enough soil heaved out each summer to 
cover the whole with an inch of new earth; and 
other similar cases elsewhere. ‘‘If the fertility 
of tens of millions of acres of land in the North- 
west, and consequently their value, has been 
mainly the work of moles [pocket-gophers],’’ 
declares Dr. Robert Bell, the Canadian geol- 
ogist, after giving proof for his thesis, ‘‘these 
