438 SIR CHARLES LYELL 



These exceptions may be compared to the accelerated rate 

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

 in which the climate and physical geography may be under- 

 going 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 prov- 

 inces 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 

 irregular in their movements. They may abandon and revisit 

 many spaces again and again, before they once approach 

 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, 

 accompanied by a constant dying-out and renovation of 

 species. 



As all the conclusions above insisted on are directly op- 

 posed to opinions still popular, I shall add another compari- 

 son, 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 

 Portici and Resina, if now covered with ashes, would overlie 

 Herculaneum. An antiquary might possibly be entitled to 

 infer, from the inscriptions on public edifices, that the in- 

 habitants of the inferior and older city were Greeks, and 

 those of the modern towns Italians. But he would reason 

 very hastily if he also concluded from these data, that there 



