6 QUARTERLY JOURNAL. 



system organic beings were to be adapted. There were controlling 

 acrents Of these, the atmosphere was one, and caloric another 

 and these have continued and will continue to control the types o 

 organization to the end of time Vary the present standard, i 

 only in a narrow compass, and but few if any of the present race 

 would continue to exist. 



In view of this subject, I hazard the assertion that the compc 



sition of the atmosphere was never essentially different since tt 



mreites of the Taconic system were created ; and also that tl 



temperature has never been greater than it is now, since that p. 



riod This is going back as far as it is possible with organ 



beings ; none older are now known to exist. Because a lizard > 



crocodile does not consume so much oxygen as an ox m a giv. 



period, it does not follow that in the era of the Lias, an era of li 



ards, the atmosphere contained less oxygen or more carbomc ao 



than it does now ; for with their respiratory apparatus, we hayi 



rio-ht to infer that if the proportion of oxygen was less than it 



at^'present, they would not be supplied with that material, a 



enouo-h could not be obtained if less existed in the atmosphe 



When we speak, therefore, of the changes which usher in a n 



system, it is not intended to inculcate the doctrine that they w 



so great, or of such a character, as would be incompatible ^ 



the present ; or that organic beings would be unfitted organicc 



for any other period or era in the world's history. 



Systems are subdivided into grotips ; the groups holding 

 same relation to a system, as the system to the totality of the c 

 solidated sediments. The beginning and end of a group is mar. 

 by some important change, such as the disappearance of affili^ 

 tribes and species. It is then by observations of this kind, 

 divisions and subdivisions of the sediments are obtained. JN: 

 which are supposed to be appropriate at the time, are confer 

 ^,pon the systems and groups. They may subsequently, hoWe. 

 be demonstrated to be inappropriate ; the progress of disco, 

 outo-rowing and thereby rendering obsolete the nomencla 

 Thi's is an^evil ; and one who is disposed to cavil, might lay 1 

 of the fact to the prejudice of the science of geology, on 

 ground that nothing is settled ; that it is a subject of opinions 

 speculations, and not of facts and principles ; of endless de 



4 



