144 RIVERS OF SOUTH DEVON. 
that it forms a sort of basin or cavity wherein our 
other strata are contained. Whatever be the nature 
and extent of the connexion maintained between 
the sea and rivers at the sources of the latter, we 
see most evident proofs of the influence of rain, 
dews, snow, &c. on their currents ; in the protracted 
droughts of June and July their fountains are no 
longer productive of due supplies to many of them, 
the fish resort to the few shallow pools that remain 
here and there in the beds of the streams, nearly 
all our springs are exhausted, vegetation altogether 
languishes, and is seemingly alone sustained by the 
dews of night ; in the fine dry weather of May when 
our rivers are at a medium of size, they will in the 
space of two or three hours swell prodigiously with 
foul water, rain having then fallen to great extent 
somewhere near their sources; the size and num- 
ber of tributary streams controuling of course the 
volume and rapidity of these torrents; the dark 
brown colour given to the rivers on these occasions 
(due in part to carbon held in solution, and derived 
from decomposed vegetable matter,—the result of 
previous hot weather, and in part to the vast 
abundance of dirt, which the increased volume 
and power of the rivers hurries forward with them) 
is by their great rapidity then acquired, often con- 
veyed out to the very mouths a considerable distance 
into the salt water; in October and November, 
which may be termed rainy months, we are again 
inundated, springs overflow, and fresh ones discover 
themselves in various directions, even breaking 
forth in hard turnpikes; in frosty weather the 
rivers are low, exhalations being in great measure 
suspended, and the hardened ground at the sources 
of the parent streamlets not suffering the vapours 
and snow to penetrate and commit themselves to 
the currents. Mountains and hills are known to be 
