E A R T H. 
«ovv above it, a change mull have happened in their com¬ 
parative level. Therefore, if any phenomenon can lead 
ns to eftimate how long it is fince that change of level 
took place, it will be a new means of difcovering the are 
of our continents. The level of the fea , whatever be its 
abfolute height, is the lowefl, and (ceteris paribus) the 
warmejl part of the atmofphere ; it was fo before the revo¬ 
lution, and it remained the fame after it. But in refpebt 
of our mountains, a great change happened: fupp'ofing 
that their tops were already ijlands in the former Jea, or 
that they were (till under it, at that epocha, either by the 
fca fubliding, or 1 y their rifing, they were placed in a 
colder region of the atmojphere ; and consequently, every 
effeft proceeding from that diflinct new circumfiance, 
began, at that time: a temperature often near the freezing 
point on the tops of high mountains, (of the Alps, for in- 
ftance,) produced frequent falls of fnow, the thawing of 
which happening to be lefs than its produbtion, the 
yearly excef's of this, transformed partly into a fpongy 
ice, began to clog their upper valleys, and to cover the 
inclined Surfaces that could retain it. When thofe accu¬ 
mulations had much increafed, the weight of the ice 
made it ilide down ; which was effected by the ice thaw¬ 
ing on its (ides, which difengaged it from the rocks, and 
by its breaking acrofs the (lopes, from its tendency down¬ 
wards. In that manner, the accumulated ice entered va¬ 
rious channels, through which it (Tided down in the form 
of lavas-, and when it had attained a. warmer region, it 
there thawed, rapidly, every Summer. That date of the 
accumulations of ice in the Alps, which brought them 
on the whole to a regular progrefs of increafe, was pro¬ 
duced after a certain time ; and as it (till continues, it 
becomes a new chronometer, absolutely independent of 
thofe that we have confidered before. The fader thaw¬ 
ing of the ice, when it has attained the lower valleys, 
depending in many refpedts on local and accidental cir- 
cumdances, does not afford a jud idea of the progrefs of 
the ice in thofe mountains : on the whole, it would there 
appear at a dand, the lavas of ice, called glaciers, Some¬ 
times advancing, at other times retreating : but that pro¬ 
grefs is very obfervable in the upper parts; for each ge¬ 
neration tranfmits to the following, fome account, either 
of the formation of new lading heaps of ice, or of the 
extenfion of old ones, fo as to fill up paffages which till 
then had remained open; and many ftich ligns of conti¬ 
nued increafe, are even within the memory of individuals. 
Therefore, it is impofiible to fuppofe, that our continents 
are very old ; for, if that were the cafe, the upper region 
of thofe mountains, in every part that could retain ice , 
would be at this time incruded with-it. 
From the revolution which produced our continents, 
another alteration happened on the furface of our globe 
relating to temperature, the caufe of which is not here my 
objedt, except, in this refpect, that it is quite diderent 
from the former; as for the effect, it is an accumulation of 
ace in the polar regions, which is dill going on. We have 
alfo fome meafure of a rate of progrefs in this effect; on 
which I (hall only quote the following paffage, in a paper 
written by Dr. Blagden, Phil. Tranf. vol. lxxiv. p. 231. 
“ Since our northern navigations, the coad of IVcf Green¬ 
land, and its furrounding feas, have gradually become 
more and more inaccejfible on account of zee.” Here then, 
sbfervation embraces alfo a proportional part of the whole 
effect, from which we may conclude, that, with fo rapid 
a progrefs, if our continents were very old, all thofe coafls 
would be inacccfjible. It might be (aid, from Buffon’s 
hypothefis, that our globe is cooling; which would ac¬ 
count for undetermined progreffes of ice: but that in- 
confident naturalid has acknowledged, that the very re¬ 
verie is the refult of a companion between recorded 
fymptoms of temperature in ancient times, and what w'e 
obferve now. Befides, that objection is precluded by 
various fubordinate phenomena of the growing ice, fome 
of which have been pointed out by M. De Saussure, 
who, from-a long and attentive ftu.dy.of the Alps, has 
i 
m 
formed the fame conclufion that I have in refpeft to the 
age of our continents. 
I have faid, that no large fragment of rock can be re¬ 
moved, by the impulfe of water , from the upper valleys 
of the Alps ; fince thofe valleys themfelves, and every 
channel from them to lower valleys, are filled with ice: 
but fome of thofe fragments, and very large ones, are 
tranfported on the ice itfelf. Thofe blocks fall on the ice- 
from the deep (ides of the adjacent mountains ; and it, 
by their acquired velocity, they roll over its'furface, fo 
as to attain fome part of its (luggifh fiream, they follow it 
down to the next low valley, and are there depolited on 
thofe (pots where the ice entirely thaws under them. 
There is always fome fitch block on its long journey down ; 
and it is efpecially from obfervations on their march, that 
the (low motion, downwards, of the whole mafs of ice, 
has been difeovered, and in fome degree determined. 
M. De Saussure explains that procefs, and then adds: 
“ From thefe blocks, accumulated at the end of the Glacier- 
des-bois, (valley of Chamouny ,) refults an important remark. 
Confidering that they are depofited on that (pot as the 
ice thaws which brings them down, it is furprifing that 
they are not in greater number. That fabt, concordant with 
many others which IJhallfuccefively mention, leads us to think 
with M. De Luc, that the prefent (late of our continents 
is not fo ancient as fome philofophers have conceived it.” 
See Voyages aux Alpes, feCt. 625. 
You may judge now, fir, that it was not fo difficult as 
you thought, to find fome means of enquiring into the - 
age of our continents: it required only to refledt on the 
various effects that were to begin at their origin ; and then 
to fix on fome fuch an effedt, the progrefs of which might 
be obferved, and to apply to that observation: I have 
deferibed fome of thofe eftedts, and their refult; but al- 
moft every phenomenon continuing, progreffively, on the 
furface of our continents, might, from fome connedtiou 
with time, and fome fign of beginning, afford materials for 
the fame enquiry; I was therefore obliged to confine my- 
felf to fome general chides of objedls, and I (hall only 
add one more. I mud obferve firll, that fince it is al¬ 
ready evident that our continents arc- not of an unbounded 
antiquity, none of the theories which fuppofe their pro- 
dudtion to have relulted from fome fow progrefs, can be 
fupported for an inftant; as thereby the imaginary caufes 
to which thofe progreffes are attributed, are brought too 
near 11s, for remaining hidden under the veil of time paf. 
Therefore, I fet afide thofe theories, which have no foun¬ 
dation whatever; and I take for granted with you, that 
the fea has changed its bed by the fudden aciion of fome 
powerful caufe: which propolition, as one of the mod 
important in geology, I (hall alfo diredtly prove in the 
courfe of the following examination. 
When vegetation was generally fpread over the furface 
of our continents, the decay of plants began to form a layer 
of a particular earth, nearly the fame over evety kind of 
original foil, and always perfectly diffindt from it : it is 
a blackifh dufl, bound by the roots of vegetables which 
continue to grow over it. I pafs by the fonfs, as there 
the work, of vegetation is too obfeure; I (hall then men¬ 
tion only, that it appears, iu that refpect, that fome 
forefls were firft produced on grounds where they could 
not continue. Some decaying forefs of oaks are recorded 
in Germany, and even in fome parts there remain (cattered 
Hunted oaks, on grounds where it has in vain been at¬ 
tempted to renew them ; but I fital 1 confine ntyfclf to 
open countries. Heath Itas been the predominant plant 
over fandy grounds in hills and plains, and common grafs 
on the fiat fummit of mountains, and on rocky and clayey 
foils at a finaller elevation. Many and very exrenfive 
parts of our continents are (till totally undifturbed : I have 
vifited fome of them jn various parts of Europe; and a 
great part of Afia is (till in that (rate. In.the countries of. 
that nature which I have vifited, and on grounds that, ever 
fince they exifted, remained in the hands of Nature, the 
w hole of the vegetable layer is found under the fpontanepus 
V torfi . 
