A R T H. 
land.) 2d. A river may have much gravel in its bed, 
though the land near it has very little: but the bed of 
fuch river is much below the fitrface of the land, and 
the gravel it contains is no more than might be contained 
in the mafs of the land that has been dug away. 3d. The 
gravel of many rivers bears no refemblance to any of the 
hard f rata that it has pervaded in its courfe : it is fome- 
times a gravel of flint, though there are no chalk Jlrata on 
its banks; it is frequently of primordiary fones, even in 
large blocks, though there are no mountains nor Jlrata of 
th 6 feJ 2 ori.es even to a great diftance : but the fame gravels 
and blocks are in the adjacent land. 4th. The bed ot fome 
rivers is gravelly in fome parts, and without gravel in other 
parts, alternately ; and this again is found in the grounds 
correfponding to thefe different parts of the river. The 
confeqttences of thefe fafts are as obvious in themfelves, 
as great in the theory of the earth, iff. It is evident, that 
the gravel depofited in the bed of rivers flowing in the 
plains was before in that part of the ground which they 
have furrowed in forming their channels. 2d. Since 
thofe rivers have no other gravel but what proceeds from 
the plains themfelves, it is evident alfo, that the plains 
cannot have been formed from the ruins of mountains', for 
thofe ruins ought to have been fpread over them by thefe 
very rivers which, on the contrary, rob them in cutting 
their channels. 3d. Confequently all the gravel of the 
plains is come out of the fea, as well as every other of 
their jirata, when our continents were left dry. 4th. But 
no gravel goes to the fea from our continents; fince rivers, 
which have gravel in fome parts of their bed, do not even 
move it along with their whole courfe. This laft confe- 
quence, which relates to the main objeft of all our pre- 
fent enquiries, will be more and more afcertained, by the 
following confiderations and fadts. 
When water has a free paffage along or above fome 
obftacles, without bending much its courfe or rifing fen- 
fibly, a part of it remains ftagnant between thofe ob¬ 
ftacles, and the reft glides over it as it would upon a folid 
and fmooth body. This is the reafon why, in following 
the courfe of moving water from the tops of the mountains, 
we have feen it driving materials before it, when it was 
obliged to rife ; and leaving them on its bottom wherever 
it could fpread: it is alfo the reafon why, when a river 
which flows in a plain, happens to drive /and and gravel 
from fome narrow path, thefe fubfide in wider parts, and 
the gravel is buried in the fand. The refiftance found 
by water, in a well-fettled bed, from its flowing over a 
nearly horizontal plane, is fufficient to determine its 
principal current in the parts above ; and the growth of 
aquatic plants upon the bed of fuch rivers is a clear 
proof that they do noffeven drive the fand which lies on 
that bottom. But there are few rivers which do not ftili 
drive fome fand in fome parts of their courfe ; and this 
proceeds from their having cut deeply fome parts of the 
ground, when they firft formed their beds. There the 
rivers cannot fpread : in floods they attack thofe fteep 
banks; and, at every fall of new materials, either by 
thefe attacks, or by the waters filtrating in the ground, 
they rife againft them, and drive them along, till they 
find a fpace to fpread, where all thofe materials fink and 
remain. But in time thofe feep banks will give way, the 
rivers will find fpace to fpread along their whole courfe, 
their fmoothed banks will be covered with vegetatun, and 
in their very floods they will, as the Adour , even Jpare a 
blade of grafs ! 
Let us now go to the fea, to meet there the rivers loaded 
with the whole of the depredations made upon our con¬ 
tinents by every moving water. ‘‘We never fee, you fay, 
p. 295, a river in a flood, but we muft acknowledge the 
carrying away of part of our land.” This is true; but 
we are now enabled to eftimate that part, and to deter¬ 
mine how far it may favour your theory of the earth. If a 
river , at its coming into the Jea, does not meet on the 
toaf with a gravelly and fandy ground, the only materials 
that it brings out of our continent, as the total refult of 
all the caufes which aft upon the grounds whence its 
waters proceed, are nothing but mere duf, as may be cer¬ 
tified by the inhabitants of the coafts near the mouth of 
every river. No gravel, nor even fand, is gathered there, 
but what proceeds from the coaft itfelf; and we have 
feen the reafons of that fadft, in following the moving wa¬ 
ters from the higheft to the lowjl grounds. Duf then is 
the only foi't sf material that our continents could furnifh 
to future ones, from the waters moving on their furface ; 
and that provifion, inconfiderable as it is even now, is 
temporary : it proceeds only from the beds of the rivers 
not being yet wide enough in every part, nor their banks 
fo fmoothed, as to prevent their ftili hurting the ground 
in fome parts of their courfe. But thofe very demoli¬ 
tions are the work of rivers for fettling their bed ; which 
operation fhall be completed without a fenfible lofs of 
the mafs of our continents ; and a time will come, when 
the lofs of fome duf, that they may continue to undergo 
in great floods, will be more than compenfated, by the 
acquifition they conftantly receive all over their furface, 
from the increafe of vegetable earth, a product in which 
water and air enter as ingredients. From that collection 
of fafts, which are within the limits of our infpeElion, it is 
evident, that no materials can be expefted from our con¬ 
tinents for new ones, by the natural caufes adding over their 
furface. What remains then to examine is, the imme¬ 
diate effeft of the fea in that refpeft ; a part of which, 
in your opinion, is contained in the laft of the hypothefes 
which I have enumerated before. 
5th. Hyp. The moveable materials delivered into the fea are 
there by the agitation of the water, carried farther and farther 
along the fielving bottom of the fea, towards the unfathomable 
regions of the ocean .—The propolition I am going to efta- 
blifh in that refpeft, from theory, and from facds, is, that 
upon every fielving fore, where the declivity is fmall, 
the agitation of the water, inftead of carrying materials 
from the coaf towards the bottom of the fa, carries them, on 
the contrary, from the bottom of the fea towards the ccaf ; and 
that there is a degree of declivity in which there is no ten¬ 
dency to alteration. You mention three forts of agita¬ 
tions of the fea ; the tides, the current, and the waves: the 
firft of which, however, will, 1 think, appear to you in¬ 
capable of any immediate erfeft, if' you conlider how 
flow the water rifes and falls upon open (helving (bores : 
in the firft of thefe motions it brings along fome fea- 
weeds floating in the water, and it leaves them moftly on 
the (hore. 1 think it then fufficient to examine the ope¬ 
rations of the currents (another effeft of the tidesJ and of 
the waves. 
Currents never reach fuch fores with any perceivable 
degree of aftion, except againft capes, which they only 
tend to round : and when thofe projeftions have acquired 
a fufficient degree of obliquity, the currents move nearly 
in a parallel direction with the coafl, at fome diftance 
from the (hore, having no other effeft than that of tend¬ 
ing conftantly to fmooth it. The whole aftion of the fea 
upon the coafs is then concentrated in the waves: it is 
almoft only by their means that the tides and currents 
have fome influence in that aftion; and this is, becaufe, 
when the water is higher, the waves reach farther upon 
the (hore. Let us then confider the effeft of that caufe. 
If the wind blows from the coaft, the fea is not agitated 
near it; there are hardly any waves: and if it blows 
againfi the coaft, the impulfe of the waves being in that 
direction, tends to roll the materials from the bottom towards 
the fore; by which foals are firft produced, and the fraud 
extends by degrees. This is known upon every fielving 
(hore; and I will give you fome inftances of that opera¬ 
tion. It is by the fea-fand carried up in that manner, that 
the formerly main branch of the Rhine, which paffed 
through Holland, has been flopped. It is by the fame 
operation that the accefs of moft part of the fea-ports, 
along the coaft of the North Sea, and of many others, 
would be flopped, if roads were not kept open by great 
labour. In the fame manner are the fediments of the rivers 
accumulated 
