The possibility of the existence of a large island or continent, midway between the Old and New World, within the traditional period, is included in the important question, which is still _sub judice_ amongst geologists, whether the general disposition of land and water has or has not been variable during past ages. Sir Charles Lyell held the first view, and was of opinion[127] that complete alternations of the positions of continent and ocean had repeatedly occurred in geological time. The opposite idea has been suggested at various dates by eminent authorities, suggested rather than sustained by elaborate arguments, until recently, when the question has been re-examined by Mr. Wallace and Dr. Carpenter. The former, in that chapter of island life devoted to the permanence of continents, dwells forcibly upon Dr. Darwin's inference from the paucity of oceanic islands affording fragments of either Palæozoic or Secondary formations "that _perhaps_ during the Palæozoic and Secondary periods neither continents nor continental islands existed where our oceans now extend; for, had they existed, Palæozoic and Secondary formations would in all probability have been accumulated from sediment derived from their wear and tear; and these would have been at least partially upheaved by the oscillations of level which must have intervened during these enormously long periods. If, then, we may infer anything from these facts, we may infer that, where our oceans now extend, oceans have extended from the remotest period of which we have any record; and, on the other hand, that where continents now exist, large tracts of land have existed, subjected no doubt to great oscillations of level, since the Cambrian period." I am not aware whether Dr. Darwin has expressed himself more authoritatively on this point in later works, or whether the whole question has been discussed in detail otherwise than by Mr. Wallace in the chapter referred to, in which he quotes what must, I think, after all, only be taken in the light of a suggestion as an auxiliary to the powerful arguments which he himself has enunciated in favour of a similar conclusion. There is no doubt that the paucity of any but volcanic or coralline islands throughout the greatest extent of existing oceans has a certain but not absolute significance, so far as recent geological epochs are concerned.