Observatiojis Concerning Fossil Organic Remains, 99 



stand all these difficulties, and am upon the watch against 

 such causes of deception, that introduce into geology those 

 uncertainties which we find in all the sciences, and which 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 himself, I observe in genera! ; 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 these two words imply is too great to be confounded. 

 Epoch, in my opinion, is distinguished from period under the 

 relation of duration of a greater or less extent, and also that 

 of consequences which flow from it. Period is a progressive 

 succession for a given time, during 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 som«e facts though very different 

 from each other, as regards their nature and their mode of 

 existence, have taken place in the same period; but we could 

 not say or maintain that these different facts took place at 

 the same time : they have occurred progressively, at different 

 times, though in the same period; or in other words, they 

 have taken place at different epochs in the same period. 



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- 

 ence which is calculated to impair the accuracy of our obser- 

 vations. 



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 subject which has been so 

 elegantly elucidated by M. de Humboldt. 



" But we will admit that strata widely differing from each 

 other, may be formed at the same moment, not only in differ- 

 ent parts of the globe, but even in the same place." 



I frankly avow my dissent from M. Brongniart, in the opin- 

 ion here expressed. I cannot imagine how different rocks 



