eee 
almost playful facility ; and it tore up masses of 
rock as large as houses out of old alluvial land, 
and rolled them a quarter of a mile along the 
valley. In 1810, in the state of Vermont in 
North America, a lake, one mile and a half in 
length, three quarters of a mile in width, and 
from 100 to 150 feet in depth, suddenly made a 
breach in its barrier about a quarter of a mile in 
width, emptied all its contents in the course of a 
few minutes through the breach, tore up a chan- 
nel a quarter of a mile wide, and from fifty to 
eighty feet deep, to a lower lake, drove down in 
a moment the lower lake’s retaining mound or 
barrier, ploughed up a channel of from 300 to. 
600 feet in width, and from 20 to 60 feet in 
depth, along the bottom of a valley of five miles 
of divergent streams, and dispersed its spoils 
over an expanse of plain, yet, in one of its 
| streams, retained so much power, at the dis- 
tance of seventeen miles from the bed of the 
lake, as to transport a rock of about one hun- 
dred tons in weight several rods from its bed. 
These facts, to which thousands of similar ones 
might be added, may probably induce even the 
crudest observers to ascribe to the action of run- 
ning water the configuration of a very large part 
of the present surface of the earth, and the for- 
mation or remodelling of a comparatively great 
amount of the existing arable land. 
The bed of the burst lake in Vermont has now 
the appearance and character of a Scottish haugh; 
and the margins of its banks are parallel terraces 
of similar formation and outline to the celebrated 
‘parallel roads’ of Glenroy in Inverness-shire. Nu- 
merous flats and meadowy levels in the valleys of 
hilly and undulating countries obviously seem to 
have, on the same principle, been beds of com- 
paratively recent lakes; and not a few terraced 
lines along the sides of hilly-valleys, at consider- 
able elevations above the height of the present 
water-courses, may be easily identified with the 
banks of ancient lakes. When a river passes 
through a lake on its way to the sea, it throws 
to the bottom all the heavier and larger particles 
of debris and diluvium brought down from the 
upper regions of the basin; and, if the lake be 
larger, the river, even though turbid and quite 
laden with silt, precipitates the very finest por- 
tions of its-freight, and debouches from the lake 
in a state of as great limpidness and purity as 
many a rill does from a fountain. Hence, the 
haughs and meadowy expanses which formed the 
bottom of small lakes—provided other circum- 
stances be equal—always possess a grittier or far 
less comminuted soil than such as were the bot- 
tom of large lakes. The river Rhone, on enter- 
ing the lake of Geneva, is extremely turbid, but 
on effluxing is beautifully limpid; and it has for 
many ages—probably since the general deluge— 
been purifying itself by the same process, and 
making similarly large deposits of silt, as at pre- 
ile 
7 ne 
ALLUVIUM. 
in length, and then divided itself into a number, 
the existing head of the lake, a fine tract of allu- 
vial land of nearly eight miles in length; and, if 
no serious disturbance should occur in the phy- 
sical laws under which it is acting, it will even- 
tually fill up the entire lake, even though 160 
fathoms in depth, and will convert the whole of 
its area into an expanse of rich meadow. A large 
portion of the vast and luxuriant valley of the 
Rhine, upwards of an hundred miles in length, 
between Strasburg and Worms, and bounded on 
the one side by the Vosges mountain, and on 
the other by the mountains of the Black Forest, 
is occupied to a great and unknown depth by an 
alluvial deposit of exactly the same materials 
which continue to be borne along by the river, 
and very obviously appears to have been at one 
time the bed of a lake far more extensive than 
that of Geneva. Other though smaller expanses 
of lacustrine land occur in the higher parts of 
the Rhine’s course; a considerable tract occurs 
at the head of the lake of Constance; numerous 
vast tracts, evidently coextensive with ancient 
lakes, occur along the course of the Danube, the 
St. Lawrence, and other great rivers; not a few 
tracts of manifestly lacustrine formation may be 
observed in the valleys of Great Britain and Ire- 
land; and tracts of greater or less extent may be 
seen at the head of Loch Lomond, Lough Neagh, 
Loch Erne, and other British and Ivish lakes. 
When lakes do not exist in valleys, to serve as 
recipients of travelled gravels and silts from the 
upper regions of a basin, rivers make their chief 
deposits either along their own channels, or 
athwart periodically inundated plains, or athwart 
a low seaboard, or beneath the waters of the 
ocean. 
in its course, which receives the numberless 
torrents of the northern Apennines and the 
south side of the Alps, and which traverses the 
vast plain of Lombardy to the Adriatic sea, makes 
such deep and constant deposits along its chan- 
nel that the neighbouring inhabitants have long 
embanked it to prevent inundations of their 
country, and are in the practice of transferring 
mud from its bottom to its banks, to the amount 
sometimes of one foot of depth in a season, and 
yet have been compelled progressively to increase 
the height and strength of the embankments, 
till at last all the lower part of the river’s course 
has become a vast aqueduct along the summit of 
a stupendous artificial mound, so lofty as to over- 
look the tops of the houses of Ferrara.—The river 
Nile, as is well known, has, from the earliest ages, 
periodically irrigated all the inhabited part of 
Lower Egypt, supplied it with a rich alluvial 
soil, counteracted upon it all the effects of aridity 
and incessant drought, and maintained it in a 
condition of fertility wondrously in contrast to the 
dismal and universal barrenness of the adjacent 
deserts. This remarkable stream collects nearly 
all its waters and all its rich freights of com- 
minuted soils and organic remains among the 
sent; it has already formed, immediately above , mountains and other uplands of the interior and 
I 
The Po, which has no considerable lake | 
