EARTH. 195 
thofe high grounds mnft have exided at the time when 
all the known caufes adling on our continents began their 
adtion : for, not only the power of Jireams is there at its 
minimum, but thofe high valleys are filled up with ice, 
which prevents the propulfion of any large materials by 
<waters : and as for the duji and fmall gravel, which fome- 
times come out from under that ice, they have been flop¬ 
ped in hollow places, not yet filled with them; and their 
very didindl mafs cannot account for any fenfible part of 
the cavities obferved above. However, the broken Jirata 
which furround thofe cavities are conflantly mouldering 
down : but the falling materials accumulate under them 
in the form of Jlopes, which fhew fenfibly the quantity of 
that effefl from its beginning, coeval with our continents. 
Confequfently, the degree of rapidity in the decay of thofe 
fummits, may give us a firfl idea of the time when all the 
continental caufes began to adt. On that particular, I 
fhall only ufe the expreflions of a celebrated obferver of 
the Alps, M. De SaufTure. Among other material obfer- 
vations which he has publifhed from a fortnight’s flay, in 
July 1788, on the Col-du geant, a fummit of thofe moun¬ 
tains elevated 1880 fathoms above the level of the fea, 
is the following: “The water proceeding from the 
thawing of fnow, filtrates conflantly in the crevices of the 
inclined Jirata of thofe fummits, and being expanded by 
frofl, it fplits them afunder. It is well known by all who 
frequent thofe mountains, that their rocks are cov.Jlantly 
crumbling dovsn ; but on the Col-du-geant, that phenome¬ 
non is imp re (Ted on the mind in a very forcible manner, 
by the frequency of the reports of crufhing maffesof rocks: 
I fhall not exaggerate in faying, that we did not pafs one 
hour, without hearing fuch reports as equalled the roaring 
of thunder, produced by the falls of rocks from the (ides 
cf the Mont-blanc, of the Aiguille-marbree ; and of the 
very eminence on which w r e had fixed our flation.” This 
is not a flow progrefs ; and when compared with the whole 
that has been performed, it cannot carry us far back in 
tracing its beginning. 
That fact is the greatefl of its kind exhibited on our 
hemifphere ; but the circumflances and caufes on which 
it depends, being common to a multitude of grounds, the 
fame effects may be obferved over the whole fiirface of 
the land. The vague operations attributed to running 
waters, veiled that important field of enquiry into the 
age of our continents : but attention only, with the moft 
common knowledge of the laws of hydraulics, will now 
diredt every obferver, in finding out, within his rambles 
or in his travels, many deep grounds, which muff have been 
fuch from the origin of our continents. For that purpofe 
it is fufficient to examine, whether any caitfe, belonging 
to the prefent (late of things, can have either railed the 
fleep eminences obferved, or funk the ground before them. 
Thofe objects, of great importance to geology, will be 
found, not in a few fpots, but in millions'; not in moun¬ 
tains only, but in hills and hillocks : they will be diftin- 
guifhed along Jireatns ; as the fancied effedts of thefe are 
now exploded ; by which means two particular progrejfes 
will be there obfervable, the fmoothing of originally abrupt 
chafms, and the fettling of the channel of the jlream. In 
that way of invefligation, founded on real principles, ve¬ 
getation in particular, as afeending over the Jlopes of rub- 
bijh under the decaying grounds, will afford, in alniofl every 
country, one of thofe chroncsneters. Vegetation tends in- 
ceffantly to take poffeilion of thofe Jlopes, and it is only 
protradled by the falling rubbifh. Many Jlopes are already 
fixed ; the Jlecpgrounds from which they have proceeded, 
were, either lefshigh, or moredifpofed to crumble down, 
than others: but in numberlefs fpots that operation is 
flill going on ;. and by comparing the whole that has been 
produced, as (hewn by the mafs of the Jlope, with deter¬ 
mined points in the progrefs, and examining in that re- 
fpedl, the fteps upwards of vegetation, this general con- 
clufion will be obtained every where, that our continents 
are not very old. 
If the laws affigned to fome great operation of nature 
be real, they generally are confirmed by various chides 
of phenomena, which have the fame remote caufe ; and 
here we have many confirmations of that fort. The fancT* 
and fmall gravel carried off from the great mountains, 
has been (as I have explained,) flopped in various recep¬ 
tacles, where, if it has not yet filled them up, it lies flill 
without any fenfible lofs. Thofe fpaces, as they now are 
obferved, have a general level, confiding partly of wa¬ 
ter, and partly of gathered fediments of the river: which 
la ft are as didindl as the water itfelf, from the furround¬ 
ing original boundaries of their common receptacle. The 
known lakes are the mod confpicuous indances of that 
kind ; we find, in all of them, new grounds formed round 
the mouth of every Jire. m difeharged there. The fedi- 
ments depofited by rivers, at their meeting that almod flag- 
nant water, being conduntly accumulated againd the fhore 
by the waves, are thereby railed fome feet above the 
common level of the lake, and the mod ancient parts are 
feldoni overflowed. Thefe new grounds being very fer¬ 
tile, are inhabited, as foon as, by the help of fome em¬ 
bankments, there is fafety in fettling upon them. Thus, 
traditions and records indicate the progrefs of thofe ac- 
quifitions of lands ; and if, in confulting thofe hour-glafs- 
like chronometers, we did not confider that it lias required 
more-or lefs time for the fird fediments to rife to the level 
of the water, the calculated time fince thofe rivers began 
to defeend from the mountains would fall diort of what 
we know', from clear documents of hidory, on the age of 
our continents. 
The whole of the operations performed by rivers along 
their courfe, ad'ords the fame refult in various modes; 
but here I mud confine myfelf to fuch general outlines 
as may lead to particular obfervations. It is evidently 
againd the laws of hydraulics to fuppofe, that a firetnn 
which, at its beginning, found a fucceffion of natural 
troughs in the interfedled declivity of the grounds, has 
fince changed its main courfe: but its inflections may 
have been altered ; and as this is a procefs which required 
time, it becomes alfo a chronometer. When a river, in fol¬ 
lowing fome original troughs, met with high grounds 
which flopped its paffage, it was forced to change its 
courfe; but at the fame time it attacked the obdacle 
which repulfed it, and there began an operation which 
could only end when the Jlream, having acquired a proper 
fweep, fhould ceafe to adt againd a deep bank. I diall 
not fpeak of rocky channels, as no material alterations 
have been produced in their original forms: loofe grounds 
only can fhew us the work of Jireatns; and in thefe it is 
very didinguifliable, becaufe they have really cut fome 
parts of their beds through them. When the rivers were 
fird flopped againd fuch grounds, by undermining them, 
they formed a peculiar fort of cliffs, very didindl from the 
Jleep grounds which had been produced by the convulfions 
of the Jirata before the birth of our continents-, for, in 
the fird, there is always a horizontal foil oppofite to them 
on the other fide of the river, proceeding from the heavy 
materials fallen from the cliffs which have been accumu¬ 
lated on the parts abandoned by that river. Thefe cliffs 
then, being produced by demolition, gradually retreated ; 
and the materials which continued to fall from them, ac¬ 
cumulating at their foot, began to embank the Jlream. 
Such of the clffs as thereby ceafed to be attacked, conti¬ 
nuing however to moulder down, were reduced into Jlopes, 
foon covered by vegetation-, and fo ended the dedructive 
power of the river in fuch parts, by its bed being there 
fettled. Thefe are the evident operations performed by 
rivers in theiroriginally fbort turnings ; which effects have 
been either favoured or retarded by particular circum¬ 
flances, eafily difeovered on almod every fpot. If that 
operation is completed the cliffs fird formed, are feen at 
fome didance, either cultivated or covered with verdure ; 
and horizontal grounds are found on the oppofite fide of the 
river ; and if the cliff} are flill attacked, the inhabitant 
of the fpot can generally afeertain what demolition lias 
been performed in known times. In this laft cafe, confi- 
2 . " dering 
