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Feb. 20, 1873] NATURE 305 
not be so quick an incentive as glory, but it is a nobler 
one, and gives a tone to character which glory cannot 
impart. That unflinching devotion to work, without 
which no real eminence in science is now attainable, im- 
plies the writing at certain times of the stern resolve upon 
the student’s character: ‘I work not because I like to 
work, but because I ought to work.’ In science, how- 
ever, love and duty are sure to be rendered identical in 
the end.” 
——————EE————————————e———EeEeE>E>_ > ——————————————————E—— 
THE TROGLODYTES OF THE VEZERE* 
\ HAVE come to speak to you about the Troglodytes 
of the Vezére, of that fossil population whose sub- 
terranean dwellings we are about to visit. 
Their existence dates back to a startling antiquity. We 
do not know their name ; no historian has mentioned them, 
not a vestige of them had been discovered until the last 
eight years ; and yet they are better known to us, in 
many respects, than certain nations celebrated in classical 
history. We know their mode of life, their industry, their 
arts, and all the details of their existence. Is not this the 
true history of races, a history far more interesting than 
that of their battles, their conquests, and even their dynas- 
ties? How can we know so much of a people who have 
left no trace in the memory of man, and whose very exist- 
ence would have been declared impossible twenty yearsago? 
Are they the creatures of a dream, like the celebrated 
Troglodytes of Montesquieu? No. Nothing is more 
real than our Troglodytes ; nothing more authentic than 
their annals. In the caverns which they inhabited, in 
those in which they laid their dead, have been found frag- 
ments of their meals, productions of their industry and 
arts, and remains of their bones. It is in this book that 
their history has been read ; it is with these documents 
that their past existence has been resuscitated. 
Many savants have taken part in these researches. 
Among others, Christy, the Marquis de Vibraye, M. Fal- 
coner, and our two colleagues, MM. Louis Lartet and 
Elie Massénat, deserve honourable mention ; but there is 
one name that eclipses all the others, it is that of the 
founder of human palzeontology—Edward Lartet. 
1.—Determining the Epoch 
Before speaking about a people it is well to assign it a 
place in time. But in this instance ordinary chronology 
is inapplicable. We are touching on periods of an incal- 
culable length. Since the epoch when our Troglodytes 
lived, the climate and fauna have undergone considerable 
modifications, which have been produced slowly, without 
any revolution, without violent action, under the influence 
of those imperceptible causes which are still at work in 
our own day ; and when we consider that, during the 
course of centuries of known time, these causes have only 
produced scarcely appreciable changes in our surround- 
ings, we can have some idea of the prodigious duration of 
what is styled a geological epoch. These immense periods 
can neither be measured by years, by centuries, nor by 
thousands of years; these dates cannot-be expressed in 
numbers, but we can determine the order in which the 
geological epochs followed each other, and the periods of 
which each is composed. These are the dates of the his- 
tory of our planet; and the elements of what Edward 
Lartet has designated paleontological chronology. It will 
_ suffice for us to determine our dates from the commence- 
ment of the guaternary epoch. 
_ The end of the tertiary epoch had been signalised by 
aremarkable phenomenon, of which the cause is not yet 
_ perfectly known. The northern hemisphere had gradually 
become colder. Immense blocks of ice, descending from 
the sides of the mountains into the valleys and plains, had 
* Being the substance of the Address of M. Paul Broca to the French 
Association for the Adyancement of Science, at the Session held at 
jis Eee 
covered a considerable portion of Europe, Asia, and North 
America ; and the temperature of our zone, till then tor- 
rid, had by degrees become frigid. The duration of this 
cold period, called the glacial period, was excessively long. 
After having attained their farthest limits, the glaciers 
retired considerably, then they advanced again, but with- 
out regaining their former position. This was the last 
phase of the tertiary epoch. The glacial period was nearly 
at anend. A gradual modification of temperature caused 
the melting of the ice, and the quaternary epoch com- 
menced. The glaciers, those immense masses of snow, 
hardened by time and accumulated during thousands of 
ages, produced, when they melted, gigantic torrents, 
sweeping along in their ‘powerful waves the ruins of 
mountains, flooding the plains, ploughing up the soil, 
hollowing the valleys and leaving in their track large 
deposits of sand, pebbles, and argile. From that epoch, 
called the dz/uvian, are dated our present rivers, but they 
give us in these days but a faint idea of what they were 
then. 
The extraordinary power of the water floods was above 
all remarkable during the early part of the quaternary 
epoch ; it gradually decreased from that time, but it was 
not until the glaciers had retired within their original 
bounds, until the temperature had become nearly equal to 
that of our own day, that the phenomenon of the great 
inundations ceased, and that the quaternary epoch drew 
toaclose, Since that time, we still find sand and pebbles 
displaced, and sometimes even masses of more or less 
volume torn from the sides of the valleys by the tor- 
rents, but the rivers and streams no longer bear along 
with them more than particles of clay and slime, and 
these deposits have formed alluvial soil. The whole 
period which has elapsed since the close of the quaternary 
epoch bears the name of Jresent efoch, and the soil which 
has been formed in this period is called recent soz/. It is, 
certainly, recent, if we compare it with the quaternary soil, 
but not with reference to our ordinary chronology, for 
several hundreds of ages must necessarily have elapsed 
during its formation. 
These considerations will aid us in comprehending the 
most essential facts which have served to establish the 
dates of human paleontology. These dates are deter- 
mined in the first place by pure geology, in the second by 
paleontology, and in the third by prehistoric archeology. 
The geological dates are chiefly inscribed in the valleys 
and in the plains, where the great floods of the quaternary 
epoch have left deposits in the shape of layers more or 
less regularly stratified. Except where some event has 
disturbed or excavated the soil, the layers are superposed 
in order of antiquity. The oldest are found beneath and 
are called low level ; above them are ranged the middle 
level, which succeed them, and which are, in their turn, 
covered by the layers of the upper level. dating from the 
latter part of the quaternary epoch. We find a layer 
more or less thick of recent soil, formed of accretions, 
turf, vegetable matter, &c., covering almost all the qua- 
ternary soil. 
It must suffice to explain’in a general way how the 
study of the stratification of the layers, termed strati- 
graphy, enables us to determine the relative age of the 
recent or quaternary deposits, This primary classification 
is purely geological. Thanks to the data which it fur- 
nishes, we can calculate the period of existence of those 
animals whose bones are found in the different layers ; 
these animals in their turn serve to characterise periods, 
and can thus establish the dates of certain soils, or of 
those partial deposits which do not form a part of a com- 
plete and regular stratification, 
I. Among the animals living in our land at the begin- 
ning of the quaternary epoch, some, like the mammoth, 
no longer exist save in a fossil state ; these are the extinct 
animals ; others, like the reindeer, have disappeared from 
our climate, but still live in other regions ; these are the 
