492 
pltnt's nattteal history. 
[Book XXXI. 
summer, still less so in autumn, andleastof all in times of drought. 
River- water, too, is by no means always the same in taste, the 
state of the bed over which it runs making a considerable 
dilFerence. For the quality of water, in fact, depends upon the 
nature of the soil through which it flows, and the juices^^ of 
the vegetation watered by it ; hence it is that the water of the 
same river is found in some spots to be comparatively un- 
wholesome. The confluents, too, of rivers, are apt to change the 
flavour of the water, impregnating the stream in which they 
are lost and absorbed ; as in the case of the Eorysthenes, for 
example. In some instances, again, the taste of river- water is 
changed by the fall of heavy rains. It has happened three 
times in the Bosporus that there has been a fall of salt rain, a 
phaenomenon which proved fatal to the crops. On three occa- 
sions, also, the rains have imparted a bitterness to the over- 
flowing streams of the Mlus, which was productive of great 
pestilence throughout Egypt. 
CHAP. 30. HISTOEICAL OBSEKVATION^S UPON WATEES WHICH HAVE 
SUDDENLY MADE THEIK APPEAEANCE OE SUDDENLY CEASED. 
It frequently happens that in spots where forests have been 
felled, springs of water make^^ their appearance, the supply of 
which was previously expended in the nutriment of the trees. 
This was the case upon Mount Hsemus for example, when, 
during the siege by Cassander,^^ the Gauls cut down a forest 
for the purpose of making a rampart. Yery often too, after 
removing the wood which has covered an elevated spot and 
so served to attract and consume the rains, devastating torrents 
are formed by the concentration of the waters. It is very im- 
portant also, for the maintenance of a constant supply of 
water, to till the ground and keep it constantly in motion, 
taking care to break and loosen the callosities of the surface 
crust : at all events, we find it stated, that upon a city of 
Crete, Arcadia by name, being razed to the ground, the springs 
and water- courses, which before were very numerous in that 
locality, all at once dried up ; but that, six years after, when 
43 See B. ii. c. 106. 
*3 Ajasson remarks, that just the converse of this has been proved by 
modern experience to be the case. 
The son of Antipater, then acting for Alexander during his absence 
in the East. 
