EFFECTS OF EMBANKMENTS, 
409 
nels is compensated in part by tbe simultaneous elevation of 
tlieir banks and tbe flats adjoining them, from the deposit of 
the finer particles of earth and vegetable mould brought down 
from the mountains, without which elevation the low grounds 
bordering all rivers would be, as in many cases they in fact 
are, mere morasses. 
All arrangements which tend to obstruct this process of 
raising the flats adjacent to the channel, whether consisting in 
dikes which confine the waters, and, at the same time, aug¬ 
ment the velocity of the current, or in other means of pro¬ 
ducing the last-mentioned effect, interfere with the restorative 
economy of nature, and at last occasion the formation of 
marshes where, if left to herself, she would have accumulated 
extent to which the river may be affected by the precipitation in its own 
basin, and by supplies received through subterranean channels from sources 
so distant as to be exposed to very different meteorological influences, effects 
of clearing and other improvements always going on in new countries—are 
all extremely difficult, and some of them impossible, to he known and 
measured. In the American States, very numerous watermills have been 
erected within a few years, and there is scarcely a stream in the settled 
portion of the country which has not several milldams upon it. When a 
dam is raised—a process which the gradual diminution of the summer cur¬ 
rents renders frequently necessary—or when a new dam is built, it often 
happens that the meadows above are flowed, or that the retardation of the 
stream extends back to the dam next above. This leads to frequent law¬ 
suits. From the great uncertainty of the facts, the testimony is more con¬ 
flicting in these than in any other class of cases, and the obstinacy with 
which “ water causes ” are disputed has become proverbial. 
The subterranean courses of the waters form a subject very difficult of 
investigation, and it is only recently that its vast importance has been 
recognized. The interesting observations of Schmidt on the caves of the 
Karst and their rivers throw much light on the underground hydrography 
of limestone districts, and serve to explain how, in the low peninsula of 
Florida, rivers, which must have their sources in mountains a hundred or 
more miles distant, can pour out of the earth in currents large enough to 
admit of steamboat navigation to their very basins of eruption. Artesian 
wells are revealing to us the existence of subterranean lakes and rivers 
sometimes superposed one above another in successive sheets j but the still 
more important subject of the absorption of water by earth and its trans¬ 
mission by infiltration is yet wrapped in great obscurity. 
