284 



PKOCEEDIIfGS OF THE GEOLOGICAL SOCIETY. 



of life towards its close, — ^multiplying nevertheless, upon the whole, 

 in the long ascent of successive deposits. Since a great part of the 

 palaeozoic creation was carnivorous, Trilobites even devouring one 

 another, in primordial ages, for want of other sustenance (Barrande), 

 and since all were liable to sudden external changes, violent death was 

 the ordinary or common lot, but, of course, together with the slower 

 extinction by disease, &c. The disappearance of feeding- grounds, 

 occurring more or less at the end of an epoch, although fatal, was not 

 always abruptly so ; for we frequently find, in the earlier strata of a 



Table XYI. — Increment and Decrement, 



Orders 



and 

 Grenera. 



Increment 

 Upwards. 



Decremeni 

 Upwards. 



Stationary, 

 or nearly so. 



Wales 



and 

 Siluria. 



New 

 York. 



Wales 



and 

 Siluria. 



N 

 Yo 



^_ Wales 

 ew -, 



rk .^''^. 

 Siluria. 



New 

 York. 



Plantse 



* 

 * 



... 



* 

 * 

 * 

 * 



* 



* 



* 



=1 



* 

 * 



I: 



« ... 



<■ ... 



« * 



P * ? 



■?«• 



Bryozoa 



Zoophyta 



Echinodermata 

 AtrvTja 



4 



^ 



t 



N 



Ehynchonella 

 Spirifer 



Avicula 



Euomphalus ... 

 Ambonychia ... 

 Cleidophorus... 



Trilobites 



Leptsena 





* 



Linffula 



Orthis 



Pentamerus ... 

 Modiolopsis ... 



Orthonota 



Nucula 



Gasteropoda ... 

 Murchisonia ... 

 Pleurotomaria . 

 Bellerophon ... 

 Orthoceras 



new series, several (or many) of the species belonging to the period 

 just past, the individuals having as it were struggled for existence. 



Vital power, or viability, differs greatly as we look upon it in 

 individuals, species, or genera. Of the length of life enjoyed by the 

 first of these in palaeozoic times we know nothing, and not much 

 respecting those of the present day ; but possibly that of the latter 

 may be learnt more or less exactly from the earKer or later maturity 

 of the animal, as suggested to me by Mr. T. Davidson. The com- 

 parative duration of a species is not so difiicult to ascertain ; for in 

 the majority of cases it is confined to a single phase or era. Where 



