Ch. III.] CAUSE OF VIOLATIONS OF CONTINUITY. 33 



sedimentary deposition, accompanied by the gradual birth and 

 death of species. 



We have already stated, that we should naturally look for 

 a change in the mineral character in strata thrown down at 

 distant intervals in the same place ; and, in like manner, we 

 must also expect, for the reason last set forth, to meet occasion- 

 ally with sudden transitions from one set of organic remains to 

 another. But the causes which have given rise to such differ- 

 ences in mineral characters, have no necessary connexion with 

 those which have produced a change in the species of imbedded 

 plants and animals. 



When the lowest of two sets of strata are much dis- 

 located over a wide area, the upper being undisturbed, 

 there is usually a considerable discordance in the organic re- 

 mains of the two groups ; but this coincidence must not be 

 ascribed to the agency of the disturbing forces, as if they had 

 exterminated the living inhabitants of the surface. The im- 

 mense lapse of time required for the development of so great a 

 series of subterranean movements, has in these cases allowed 

 the species also throughout the globe to vary, and hence the 

 two phenomena are usually concomitant. 



Although these inferences appear to us very obvious, we 

 are aware that they are directly opposed to many popular 

 theories respecting catastrophes ; we shall, therefore, endeavour 

 to place our views in a still clearer light before the reader. 

 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 in- 

 scriptions on public edifices, that the inhabitants of the inferior 

 and older town were Greeks, and those of the modern, Italians. 

 But he would reason very hastily, if he also concluded from 

 these data, that there had been a sudden change from the Greek 

 to the Italian language in Campania. Suppose he afterwards 

 found three buried cities, one above the other, the intermediate 

 VOL. III. D 



