Part III.] OR POISONED BY VEGETABLE GROWTH? 
formidable than its usual self, as a shotted gun is 
more formidable than an unshotted gun. We 
never see the clear torrent set its rocky ammuni¬ 
tion in movement, though the shape of this ammu¬ 
nition tells us how often, and for what distances, 
it has been projected. But when the torrent is 
turbid with the wash of rain, we can hear its huge 
cannon balls rattling down, and grinding each 
other and their rocky bed and banks till what has 
started from the mountain’s brow as a huge rock 
arrives at the sea in the form of pebbles, or of 
sand. For although, as the flood of rain subsides, 
the flow of boulder-stones ceases, this is only for 
a time: each rain sets them on a stage on their 
journey, as, in lower levels and gentler gradients, 
I have said of soil, and the more minute par¬ 
ticles formed by disintegration and vegetable 
chemistry. 
A very slight difference in hardness of surface, 
or thickness of vegetation, at the brow of the hill 
may concentrate the wash of rain into a stream; 
this forms a channel, which is fed by rain from 
its sides. And though all possible natural acci¬ 
dents of this sort might have been supposed to 
have taken place long ago in all but volcanic, or 
newly raised regions, Lyell, quoting Sir T. D. 
Lander’s account of the great floods in Moray- 
