SYNCHRONISM OF GEOLOGICAL FORMATIONS. 227 



tropical seas, was, even as late as the Eocene period, found abun- 

 dantly as far north as the fortieth and fiftieth parallels of latitude. 

 That some of the ancient faunas may represent faunas of the deep 

 sea cannot be denied ; but it appears far more probable, in the light 

 of recent investigation, that they are in the main of a littoral char- 

 acter. At any rate, that they are not comparable to the cold-water 

 fauna of the deep, which alone maintains somewhat of a uniform 

 character, is indisputably proved by the abundance of forms indi- 

 cating a high temperature. Furthermore, even the general identity 

 claimed by Sir Wyville Thomson for the abyssal fauna of the world 

 has quite recently been contested by the late Gwyn Jeffreys. 81 



Synchronism of Geological Formations. It is well known 

 that the order of deposit of the various formations, from the oldest 

 to the newest, is constant the world over, and that nowhere, except 

 where there may have been a reversal of the strata themselves, is 

 there evidence of a reversed position. Corresponding strata, as in- 

 dicated by the contained fossils, have, therefore, been considered 

 to belong to the same age, even though occurring in widely-sepa- 

 rated regions. This view, for a long time maintained undisturbed 

 by the earlier geologists and paleontologists, has been dissented 

 from by Edward Forbes, Huxley, and other advocates of the doc- 

 trine of faunal dispersion from localised areas or centres of distri- 

 bution (opponents of independent creation), on the obvious ground, 

 that faunas, starting from a given point of origination, could only 

 spread by migration, and that such migration must consume time, 

 proportioned to the distance travelled and the physical and physio- 

 graphical facilities afforded for travelling. Hence, it was argued, 

 that widely-separated formations, showing an equivalent faunal 

 facies, as, for example, the Silurian of America and the Silurian of 

 Europe or Eastern Asia, or the Cretaceous of Europe and of South 

 America, could not be of identical age, and, probably, not even 

 approximately so. In support of this position, it has been urged 

 that during the present age of the world the faunas of the several 

 continents are widely distinct, and could, under geological condi- 

 tions, be considered as indicating different zoological (geological) 

 eras. In conformity with this view, Professor Huxley has pro- 

 posed 82 the term "homotoxis," indicating similarity of arrange- 

 ment, in place of synchrony, to describe the relation of distant areas 

 of the same formation. 



