RIVER SEDIMENT. 
547 
Esjpifs Theories. 
Espy’s well known suggestion of the possibility of causing 
rain artificially, by kindling great fires, is not "likely to be 
turned to practical account, but the speculations of this able 
meteorologist are not, for that reason, to be rejected as worth¬ 
less. His labors exhibit great industry in the collection of 
facts, mucli ingenuity in dealing with them, remarkable in¬ 
sight into the laws of nature, and a ready perception of analo¬ 
gies and relations not obvious to minds less philosophically 
constituted. They have unquestionably contributed very es¬ 
sentially to the advancement of meteorological science. The 
possibility that the distribution and action of electricity may 
be considerably modified by long lines of iron railways and 
telegraph wires, is a kindred thought, and in fact rests much 
on the same foundation as the belief in the utility of lightning 
rods, but such influence is too obscure and too small to have 
been yet detected. 
River Sediment. 
The manifestation of the internal heat of the earth at any 
given point is conditioned by the thickness of the crust at such 
point. The deposits of rivers tend to augment that thickness at 
their estuaries. The sediment of slowly flowing rivers empty¬ 
ing into shallow seas is spread over so great a surface that we 
can hardly imagine the foot or two of slime they let fall over 
a wide area in a century to form an element among even the 
infinitesimal quantities which compose the terms of the equa¬ 
tions of nature. But some swift rivers, rolling mountains of 
fine earth, discharge themselves into deeply scooped gulfs or 
bays, and in such cases the deposit amounts, in the course of a 
few years, to a mass the transfer of which from the surface of a 
large basin, and its accumulation at a single point, may be 
week’s rain had been drenching the ground, and though the surface was 
whitened with snow, and though pools of water were standing upon the 
surface in the immediate neighborhood, still the everlasting subterranean 
fire was burning, and the smoke arising through the snow.” 
