o 



22 



CONCLUDINa EEMARKS ON 



[Ch. XIV. 



#■ 



e 



augment or dimmish the amount of discrepancy. Thus, at 

 some periods a pestilential disease may have lessened the 

 average duration of human life, or a variety of circumstances 

 may have caused the births to be unusually numerous, and the 

 population to multiply ; or, a province may be suddenly colo- 

 nised by persons migrating from surrounding districts. 



These exceptions may be compared to the accelerated rat 

 of fluctuation in the fauna and flora of a particular region, in 

 which the climate and physical geography may be under- 

 oing an extraordinary degree of alteration. 



But I must remind the reader, that the case above pro- 

 posed has no pretensions to be regarded as an exact parallel 

 to the geological phenomena which I desire to illustrate ; for 

 the commissioners are supposed to visit the different pro- 

 vinces in rotation; whereas the commemorating processes 

 by which organic remains become fossilised, although they 

 are always shifting from one area to the other, are yet very 



They may abandon and revisit 



once approach 



mov 



o 



and again, before they 



many spaces again 



another district ; and, besides this source of irregularity, it 

 may often happen that, while the depositing process is sus- 

 pended, denudation may take place, which may be compared 

 to the occasional destruction by fire or other causes of some 

 of the statistical documents before mentioned. It is evident 

 that, where such accidents occur, the want of continuity in 

 the series may become indefinitely great, and that the monu- 

 ments which follow next in succession will by no means be 

 equidistant from each other in point of time. 



If this train of reasoning be admitted, the occasional dis- 

 tinctness of the fossil remains, in formations immediately in 

 contact, would be a necessary consequence of the existing laws 

 of sedimentary deposition and subterranean movement, accom- 

 panied by a constant mortality and renovation of species. 



As all the conclusions above insisted on are directly opposed 

 to opinions still popular, I shall add another comparison, in 

 the hope of preventing any possible misapprehension of the 

 argument. Suppose we had discovered two buried cities at 

 the foot of Vesuvius, immediately superimposed upon each 

 other, with a great mass of tuff and lava intervening, just as 





in- 



of 



