a regular communication being kept up between 
every point and the line of greatest depression ; 
forming together a system of valleys communi- 
cating with one another, and having such a nice 
adjustment of their declivities, that none of them 
join the principal valley either on too high or too 
| low a level.” The enormous number of subor- 
dinate valleys, amounting in each case to many 
hundreds, and in some cases to several thousands, 
in the basin of almost every one of even the third 
or fourth rate rivers of the world,—the occupancy 
of them all, from end to end, by streams of the 
same direction as themselves,—their perfect re- 
lationship to one another, the short and narrow 
to the next in extent, the next to the larger, and 
the larger to the chief,—their exact common 
adaptation, by elevation, ramification, and direc- 
tion, to the purposes of a multitudinous system 
of water-course terminating in one main chan- 
nel,—the slopes or declinations of their sides, 
seldom consisting of precipices or abrupt escarp- 
ments, and usually exhibiting the precise gra- 
dient which the long and silent abrasion of the 
running and wearing streams might be supposed 
to effect,—the occasional phenomenon of ‘ par- 
allel lines’ or equally elevated terraces at some 
height along their sides, or of one or more ex- 
pansions and contractions of flat territory at 
some height along their course, marking the 
quondam existence of fluviatile lakes, which 
have long since burst through the barriers by 
which they were retained,—and the simple 
mineral constituency of the soils of the small 
and upper valleys, exhibiting the few elements 
of the rocks in the mountains at their head, the 
more compound mineral constituency of the soils 
| of the secondary and lower valleys, exhibiting 
_ the elements of the rocks at the head of the con- 
nected series of upper valleys, and the thoroughly 
compound mineral constituency of the soils in 
the terminating part of the grand main-trunk 
valley, exhibiting the elements of all the rocks, 
and all the debris, and all the moveable organic re- 
mains of the whole of the multitudinous sections 
of the basin,—these are proofs which scarcely 
any man in his senses will resist, that the valleys of 
the world, as they at present exist, were scooped 
out and fashioned by the action of running water, 
—and they, at the same time, are important illus- 
trations of the nature and formation of all the 
alluvium which constitutes a large and most im- 
portant part of the soils of valleys. 
The hard rocks which constitute the great 
mass of all mountains and hills, generally reach 
the surface of the heights which bound the upper 
parts of valleys, or are covered only by a very 
thin stratum of detritus and vegetable mould ; 
wherever they are exposed to the action of the 
weather, they are constantly undergoing dis- 
integration into new materials of detritus and 
debris ; and so steadily and rapidly do they 
yield up new disintegrations to succeed those 
which are washed away by rains and torrents, 
ALLUVIUM. | 127 
that most hill-summits may be ascertained to 
lose some inches of their altitude during any 
one man’s lifetime of observation, and many 
have been observed to lose several feet dur- 
ing the period of comparatively very few years. 
Thunder-showers, ordinary rains, and the thaw- 
ings of snow and ice, sweep down disintegrations 
and incipient soil from the summits of mountains 
to their sides; rills and torrents break up debris 
into smaller particles, and carry detritus and 
soils from the sides of mountains to the upper 
parts of the higher valleys ; brooks, rivulets, and 
freshets, triturate the gravels and soils and coarse 
alluvium of the higher valleys into gritty or half- 
pulverized earths, and bear them along to the lower 
valleys; and streams, rivers, and occasional or 
seasonal inundations comminute the soils and 
earths of the lower valleys into silts or argilla- 
ceous sands, and either spread them athwart the 
low-lying fields and meadows as rich natural 
manures and top-dressings, or career away with 
them to the seaboard, to form deltas above the 
shore, or the ingredients of future land beneath 
the tide. A continual process is thus going on 
of depressing mountains, elevating valleys, trans- | 
ferring the soils of uplands to lower grounds, 
conveying the soils of low grounds to meadows, 
deltas, and the ocean, and, in general, forming 
belts, bands, and occasional expanses of new land 
along the course, and at the mouth, of most con- 
siderable streams, and nearly all large rivers. 
Now all these fluviatile formations, whether con- 
stituting the very surface of existing land, or re- 
taining their original character in the position of 
subsoils, or lying at the bottom of estuaries and | 
bays ready to become land when they so ac- 
cumulate as to rise above the sea, are strictly al- 
luvial; and many of the first class, or those which 
constitute the surface of existing lands, will in- 
stantly be detected by all sorts of farmers as || 
identical with the richest meadow grounds and | 
low-lying arable lands of England, and with the | 
carses, the holms, and the haughs of Scotland. 
The power of rain and rills to disintegrate and | 
carry off the surface of the uplands round the || 
head of valleys, is greatly aided by dews, fogs, || 
thunder - showers, snows, frost, lichens, moss- 
plants, carbonic acid, and electricity; and this 
aid is vastly stronger, steadier, and more effec- 
tive than a cursory thinker would conceive pos- || 
sible. Nor does this power operate only to break 
up and carry off the crust of the uplands, but it 
triturates and pulverizes the debris, diluvium, 
and transported gravels of the lower grounds, 
tears up and sweeps away coarse vegetation, and 
many organic remains, combines mineral matters 
with vegetable moulds, compounds all the trans- | | 
portable materials of uplands and lower grounds, 
of the hills and the middle valleys, into the con- 
stituents of a fine fertile soil, and sends down 
the whole in the ordinary currents of the main 
streams, and particularly in freshets and inun- 
dations, to constitute, athwart the meadows and | 
