Alfred Russel Wallace : Alfred Wallace : A. R. Wallace :
Russel Wallace : Alfred Russell Wallace (sic)

 
 
The Permanence of Ocean Basins (S457: 1892)

 
Editor Charles H. Smith's Note: A letter to the Editor printed in the November 1892 issue of Natural Science. Original pagination indicated within double brackets. To link directly to this page, connect with: http://people.wku.edu/charles.smith/wallace/S457.htm


    [[p. 717]] It seems desirable that I should say a few words in reply to Dr. Blanford's letter in the last issue (p. 639), and to Mr. Jukes-Browne's article in the preceding number of Natural Science (pp. 508-513).

    Both these writers lay stress upon a supposed considerable modification of my views in my late paper. I reply that there is no real alteration; because the 1,000-fathom line was never adduced by me as an absolute and rigid boundary between the oceanic and continental areas, but as a general indication of their respective limits according to the best obtainable evidence. In proof of this, I may point out that even in the first edition of "Island Life" (p. 444) I refer to a submarine plateau at a depth of between 1,000 and 2,000 fathoms, which stretches southward from New Zealand towards the Antarctic continent, and suggest an ancient connection "with the Great Southern Continent by means of intervening lands and islands"; and in my "Darwinism" (p. 346) I define the permanence of oceanic and continental areas as meaning that, "while all of them have been undergoing changes of outline and extent from age to age, they have yet maintained substantially the same positions, and have never actually changed places with each other"; and again, at p. 347, after stating that the 1,000-fathom line "marks out, approximately, the continental area," I add: "There may, of course, have been some extensions of land beyond this limit, while some areas within it may always have been ocean; but so far as we have any direct evidence, this line may be taken to mark out, approximately, the most probable boundary between the continental areas and the great oceanic basins."

    In my recent paper I have merely repeated and enforced these statements by showing how little real difference is made by carrying the possibilities of Continental extension, in rare cases, as far as the 1,500- or 2,000-fathom line. There is, therefore, no ground for alleging any departure from supposed "extreme views" which I formerly held, since the fresh arguments I have adduced show any great extension beyond the 1,000-fathom line to be in the highest degree improbable.

    Dr. Blanford objects to my statement that the theory of the permanence of the ocean basins was "attacked" by him. Perhaps the word was not well chosen, and I should have said "criticised," but it was held by Mr. Jukes-Browne to be such a damaging criticism that (in private correspondence) he expressed surprise that I had not replied to its arguments in the new edition of "Island Life." But though the passage quoted by Dr. Blanford is not very antagonistic, there is much in the "Address" itself that is altogether opposed to my views. For instance, the writer argues in favour of a former land-connection between South America and Africa, which he says is "chiefly shown by tropical forms," though adding, "but these may have migrated far southward during warm periods;" and, later on, he speaks of a possible "girdle of land, chiefly in low latitudes, round nearly three-quarters of the globe, from Peru to New Zealand, and the Fiji Islands." But any such land-extension as this is so wholly inconsistent with the permanence of the great ocean basin of the Pacific, that to argue in favour of it is certainly to attack the theory of permanence. Again, a direct land-connection between South Africa, Madagascar, and the Peninsula of India is very strongly advocated, but the 1,000-fathom line shows us an actual though slightly circuitous connection by means of existing continental areas between Africa and India, and to hold that this would have been insufficient--why, I cannot [[p. 718]] possibly understand--and to prefer to bridge across an ocean between 2,000 and 3,000 fathoms deep, in order to reduce the distance to about three-quarters of the other route, is again to hold views totally inconsistent with the theory of ocean-permanence.

    Even in the passage from his "Address" quoted by Dr. Blanford, there is more antagonism than agreement; for I cannot admit that "there is no evidence whatever . . . that every ocean-bed now more than 1,000 fathoms deep, has always been ocean." If by "every ocean-bed" we mean the great oceanic basins as distinguished from deep seas within continental areas, and if we admit those very rare and limited encroachments of old continents on the margins of these oceans, which, as I have shown, I have always admitted, then I maintain that there is very strong evidence indeed of the permanence of all the great ocean-basins, and that the 1,000-fathom line still gives us the best indication of the general limits of the old continental areas. This is so, because the facts adduced in my last paper show that any extension of the continents into the oceanic areas much beyond the 1,000-fathom line would necessitate the submergence to great depths of many times their area of existing land.

    Before concluding, I must briefly notice a very extraordinary claim of Mr. Jukes-Browne. He says ("Evolution of Oceans and Continents," p. 510):--"Those who oppose the doctrine of permanence say that the present continents are the outcome of a long series of geographical mutations," each phase being "an episode in a long process of geographical evolution."

    But this is exactly what those who uphold permanence have always said. Dana taught the evolution of the American continent nearly forty years ago; Sir Archibald Geikie has discussed "Geographical Evolution" with permanence of continental areas; and I myself, following these great masters, have endeavoured to sketch out the process of this evolution and its results. This "process of evolution" necessarily implies permanence of position of the continental as regards the adjacent oceanic areas--the only permanence that has ever been postulated by myself or others, and it is simply amazing to find this very process now claimed as if it were the discovery and the distinctive teaching of those who oppose permanence!

    In conclusion, I may say that, while admitting with pleasure the growing approximation of views on this subject, I cannot forget that it has been, and still is with many writers, the practice to assume former continental extensions across the great oceans in order to explain difficulties in the distribution of single genera or families; that geologists of repute have claimed the Dolphin bank in the Atlantic trough as the relic of a chain of mountains comparable with the Andes; that oceanic islands have been recently claimed to be merely the tops of submerged mountains, which can only be properly compared with the highest points of continents, and that a geological critic so late as 1879 considered the idea that the oceans had always been in their present positions "a funny one." If such extreme views are now less common than they were, I hope that I may, without presumption, claim to have had some share in bringing about the change in scientific opinion now in progress.


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