160 ROBERT BELL ON THE CAUSES OF THE 
The formation of the vegetable mould in these regions must, therefore, be due to some 
other agency than that of worms, and this I believe to be principally the moles, which 
live in vast numbers throughout the region in question and, although apparently insig- 
nificant animals, accomplish more in the way of soil-making than the earth-worms of 
England. There appear to be three or four different species of them. In my first jour- 
neys across the prairies, I was struck with the immense amount of work carried on by 
these industrious little creatures, and of the great effect of all this in the aggregate. In 
my report for 1874, page 32,1 called attention to this fact, where, in speaking of the 
Assiniboine country, I mentioned that “in the prairie-portions, the moles have thrown 
up almost every foot of the soil into little hummocks, often for miles in extent.” The 
mole-hills here mentioned were the fresh ones of that season. Since the year referred to, I 
have had abundant opportunities for studying these phenomena, and I am convinced that 
the moles’ work is the main cause of the great fertility of the prairie-regions of the North- 
West. In one season a single mole will throw up a great number of these little hum- 
mocks, each containing a large shovelful of earth and burying completely the grass and 
other vegetation over a space of a square foot and upwards. The vegetable matter, thus 
buried, decays and becomes incorporated with the soil. This process is analogous to that 
of turning over the sod with a plough, or of ploughing under a crop of clover or buck- 
wheat, sown for the express purpose of being thus used to manure the land. It is well 
known that the darkness of colour in any soil is increased through long cultivation, 
accompanied by the annual ploughing into it of stable manure or green herbage, whereas, 
without this addition, the land becomes lighter in colour, and after a time, almost sterile, 
as has happened to some of the once productive farms between Montreal and Quebec. 
The work of the moles not only enriches but also refines the soil. In making their 
burrows, they select the finer material and cast it up to the surface, leaving behind the 
larger stones, and as much of the gravel as possible. The effect of this in the course of 
time is the same as that of the work of the earth-worms ; namely, to cause all the stones 
to be sunk beneath a layer of nearly uniformly fine and dark-coloured material. 
The slightly hummocky surface, due to the work of moles, may be said to be almost 
universal over the most fertile prairie-lands of the North-West. In driving along a well- 
beaten trail, one may not notice this peculiarity, but the moment he turns off he will 
remark the lumpy nature of the ground. It is also very observable where the prairie 
has been recently swept by fire. The mole-hills are so thickly scattered, that by careful 
observation it will be found that, including the old ones as well as the new, they actually 
touch each other im all directions. In the autumn, after a fire, the burnt ends of the 
prostrate grass may be seen thickly projecting all around from beneath the fresh mole- 
hills. There is no doubt that the same soil has been turned over many times by the moles, 
always becoming finer and finer as they have eliminated more and more of the coarser 
material at every digging up. A fresh attack by an army of moles may sometimes be 
observed upon a piece of ground from which they had retired years before, as shown by 
the absence of any recent burrows amongst thousands of old ones. Thus large patches of 
new mole-hills alternate with others of the last or previous years. This rotation of bur- 
rowing grounds may be due to their varying dampness through a series of years. I have 
seen old mole-hills thickly studding the bottoms of ponds which would be permanent 

