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Show 32 EFFECTS OF DENUDATION • [Ch. III. If, 1~ or examp1 e , a1 1 the registers are m. ade in a single ye. ar, the propor tw. n o f deaths and births will be so smal.l durmg t h e m· terv a1 b e t we en the compiling of . two conse. cutive docu-ments, t h a t th e I' ndividuals described m each w11l be nearly 'd · 1 1 as 1'f there are sixty provinces, and the survey 1 entiCa ; w 1ere , . . of eac h reqm· re s a yea1• there will be an almost entire dtscord- w ' • • • ance between the persons enumerated m two consecutive regis-ters. . There are undoubtedly some other causes bestdes the mere quantity of time which may augment or diminis~ the amou~t of discrepancy. Thus, for example, at some periods a pestilential disease may lessen the average duration of human life, or· a variety of circumstances may cause the births to be unusually numerous, and the population to multi~ly; ~r, a pro: vince may be suddenly colonized by persons mtgratmg from surrounding districts. We must also remind the readet·, that we do not propose the above case as an exact parallel to those geological phenomena which we desire to illustrate ; for the commissioners are supposed to visit the different provi~ces in ro~ation, ~hereas the commemorating processes by whiCh orgamc remams become fossilized, although they are always shifting from one area to another, 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 suspended, denudation m~y take place, which ~a~ be compared to the occasional destructiOn 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 monuments 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 frequent distinctness of the fossilremuins, in formations immediately in contact, would be a necessary consequence of the existing laws of 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 occasionally with sudden transitions from one set of organic remains to another. But the causes which have given rise to such differences 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 dislocated over a wide area, the upper being undisturbed, there is usually a considerable discordance in the organic remains 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 immense 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 inscriptions 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 |