16 THE OPEN BOOK OF NATURE 
of stuff has been moved from the road by running 
water in a few hours. If the process were to go on 
at the same rate for a few years, there would be 
little of the road left—the grit would be washed 
from its present position, and laid down elsewhere. 
The road-menders, however, take care that more 
cinders are laid on the road from time to time, and 
thus the loss is made up, and the accumulated 
deposit is removed by the cleaners. 
I would have you observe, also, what a cleanly cut 
and neat channel the little stream has made. There 
it takes a straight course for a few feet, and the 
sides of the channel are vertical and cliff-like. If 
you were no bigger than a cockroach, and were at 
the bottom of the channel, the sides would appear 
like great precipices. There is a bend in the stream- 
let, and on the right side the water has carved a little 
cliff, while on the left, in the angle of the bend, it has 
formed a gently sloping deposit of fine grit. 
Loads of coarse cinders are spread over this road 
in winter-time. The cinders are full of little holes, 
and these get filled with water during rainy periods. 
When frost comes, the water in the cinders freezes. 
When a thaw follows, the cinders break up into fine 
grit, and the road becomes very muddy. How 
does this come about ? Well, you know water ex- 
pands when it freezes, and the frozen water in the 
coarse cinders breaks them up into small particles, 
which, however, hold together so long as the frost 
lasts. When the thaw comes the particles are 
Separated, the coarse cinders are thus reduced to 
fine grit, which, soaked with the thawed water, 
makes a most objectionably dirty road. 
