a causes J pierre teat narod into 0 geology t 10s 
uncertainties which we find in all the sciences, and which 1 re- 
quire of the geologist, constant attention and labor, in order 
to select those species from which he ought to draw his char- 
acters, and to attach to them their due importance.’ 
Remarks upon this reply. 
Upon the reply of M. Brongniart to the question proposed 
by himeelf I eheotes e in general ; and in the first place, that it 
appears to me he does not make a distinction between the 
words period and epoch; yet the difference between the ideas 
which tee two words ‘imply i is too great to be confounded. 
Epoch, in my opinion, is distinguished from period under the 
relation of duration of a greater - less extent, and also that 
of consequences which flow from eriod is a progressive 
succession for a given time, salen which many acts succeed 
each other, or many developments take place at different 
times and remote from one another. In consequence of 
this distinction, we say that some facts though very different 
from each other, asregards their nature and their m 
existence, have taken place in the same —s but we sem 
not say or maintain that these different facts at 
the same time: they have occurred progressively, at vigerent 
times, though in the same period ; or in other words, they 
have taken place at different epochs i in the same 
By neglecting this logical distinction, we make events con- 
temporaneous, which have occurred at epochs quite distinct, 
and therefore introduce a degree of confusion into the sci- 
enc which i is calculated to impair the accuracy of our obser- 
We can say that various formations may have been form- 
ed in the same period, but we cannot say that these same 
formations were formed at the same epoch: such an error 
would undermine the foundations of the science as relates 
to the superposition of rocks; a vena which has been so 
elegantly elucidated by M. de "Humbo 
“ But we will admit that strata wey differing from each 
other, may be formed at the same moment, not only Jin differ- 
