944 DAMAGE BY INUNDATION. 
times during the historic period; and our acquaintance with 
the forest topography of ancient Gaul or of medizeval France is 
neither sufficiently extensive nor sufficiently minute to permit 
us to say, with certainty, that the sources of this or that partic- 
ular river were more or less sheltered by wood at any given 
time, ancient or medizeval, than at present.* I say the sources 
of the rivers, because the floods of great rivers are occasioned 
by heavy rains and snows which fall in the more elevated re- 
gions around the primal springs, and not by precipitation in the 
main valleys or on the plains bordering on the lower course. 
The destructive effects of inundations, considered simply as a 
mechanical power by which life is endangered, crops destroyed, 
and the artificial constructions of man overthrown, are very 
terrible. Thus far, however, the flood is a temporary and by 
no means an irreparable evil, for if its ravages end here, the 
prolific powers of nature and the industry of man soon restore 
what had been lost, and the face of the earth no longer shows 
traces of the deluge that had overwhelmed it. Inundations 
have even their compensations. The structures they destroy 
are replaced by better and more secure erections, and if they 
sweep off a crop of corn, they not unfrequently leave behind 
them, as they subside, a fertilizing deposit which enriches the 
exhausted field for a succession of seasons.t If, then, the too 
* Alfred Maury has, nevertheless, collected, in his erudite and able work, 
Les Foréts de la Gaule et de Vancienne France, Paris, 1867, an immense 
amount of statistical detail on the extent, the distribution, and the destruction 
of the forests of France, but it still remains true that we can very seldom 
pronounce on the forestal condition of the upper valley of a particular river at 
the time of a given inundation in the ancient or the medizval period., 
+ The productiveness of Egypt has been attributed too exclusively to the 
fertilizing effects of the slime deposited by the inundations of the Nile; for 
in that climate a liberal supply of water would produce good crops on almost 
any ordinary sand, while, without water, the richest soil would yield nothing. 
The sediment deposited annually is but a very small fraction of an inch in 
thickness. It is alleged that in quantity it would be hardly sufficient for a 
good top-dressing, and that in quality it is not chemically distinguishable 
from the soil inches or feet below the surface. But to deny, as some writers 
have done, that the slime has any fertilizing properties at all, isas great an 
