walcott. ] CORRELATION. 427 



of the faunas, in connection with a careful study of the sedimentation 

 and stratigraphy, will make our present methods appear to have been 

 lacking in scientific precision. 



Contemporaneity and Romotaxis. — When it was once established that 

 a certain orderof succession of fossils occurred in Europe, it was con- 

 cluded that identical or similar assemblages of organisms would be 

 found to prevail elsewhere over the earth ; and that the geographic 

 distribution of each successive fauna was world-wide, each fauna being 

 a new creation. The present view is, that the chronologic succession 

 of the fauna is local, as proved by the existence of zoologic provinces, 

 and that each fauna is descendant from some preexisting fauna. This 

 result is modified for each province by the migration of faunas and 

 portions of faunas from province to province. Notwithstanding the 

 various elements that influenced the evolution of the faunas, it is found 

 that the general succession of species and faunas is in the aggregate the 

 same all over the world, however much it may have been broken, ad- 

 vanced, or retarded in certain areas in ancient or relatively recent 

 geologic time. 



Prof. Huxley, when introducing the term " Homotaxis," said: 



Edward Forbes was in the habit of asserting that the similarity of the orgaDic con- 

 tents of distant formations was prima facie evidence, not of their similarity, but of 

 their difference of age ; and holding as he did the doctrine of single specific centers, 

 the conclusion was as legitimate as any other; for the two districts must have been 

 occupied by migration from one of the two, or from .an intermediate spot, and the 

 chances against exact coincidence of migration and of imbedding are infinite. 



Iu point of fact, however, whether the hypothesis of single or of multiple specific 

 centers be adopted, similarity of organic contents can not possibly afford any proof 

 of the synchrony of the deposits which contain them; on the contrary, it is demon- 

 strably compatible with the lapse of the most prodigious intervals of time, and with 

 interposition of vast changes in the organic and inorganic worlds, between the epochs 

 in which such deposits were formed. 1 * * • 



There seems, then, no escape from the admission that neither physical geology nor 

 paleontology possesses any method by which the absolute synchronism of two strata 

 can be demonstrated. All that geology can prove is local order of succession. It is 

 mathematically certain that, in any given vertical linear section of an undisturbed 

 series of sedimentary deposits, the bed which lies lowest is the oldest. Iu any other 

 vertical linear section of the same series, of course, corresponding beds will occur in a 

 a similar order ; but however great may be the probability, no mau can say with abso- 

 lute certainty that the beds in the two sections were synchronously deposited. For 

 areas of moderate extent, it is doubtless true that no practical evil is likely to result 

 from assuming the corresponding beds to be synchronous or strictly contemporaneous ; 

 and there are multitudes of accessory circumstances which may fully justify the 

 assumption of such synchrony. But the moment the geologist has to deal with large 

 areas or with completely separated deposits, then the mischief of confounding that 

 "Homotaxis" or " similarity of arrangement," which can be demonstrated, with 

 " synchrony " or " identity of date," for which there is not a shadow of proof, under 

 the one common term of " contemporaneity " becomes incalculable, and proves the 

 constant source of gratuitous speculations. 2 



» Quart. Jour. Geol. Soc, London, vol. 18, 1862, p. xlv. 

 2 Op. cit.,p. xlvi. 



