Abstract
IN Dr. Hobson's letter on this subject, he confuses the argument by the introduction of a new factor (never alluded to in the former discussion, or in my theory as stated in “Island Life”), the bulk or volume of the matter deposited. This has nothing whatever to do with the practical problem, because it is admittedly impossible to form any estimate of the total bulk of all the stratified rocks of the earth during all geological time; while it is equally impossible to form any estimate of the total bulk of the denuded matter, since we have no clue whatever to the number of times the same areas have been again and again denuded. But the maximum thickness of the same rocks, compared with the average rate of denudation, and the coincident maximum rate of deposition, do furnish materials for an estimate, since they can all be approximately determined from actual observation; and the result is what I have given. If Dr. Hobson had referred to the former discussion he would have avoided imputing to me “fallacies” which I never made. I never said a word about “equal bulks” of material being deposited in less time than they were denuded. But, as the only available data are those of thickness, not bulk, then it is clear that, if the area of deposition is one-nineteenth of the area of denudation, the rate of deposition of a known thickness of rocks will be nineteen times as great as the known rate of denudation. It was necessary for me to point this out when first discussing the subject, because one eminent writer had made the rate of deposition less than the rate of denudation, because the water-area is greater than the land-area of the globe; while an eminent geologist has quite recently taken the rates of denudation and deposition as being equal. If, however, the area of deposition is very much less than the area of denudation, which is now admitted to be the fact, then the rate of deposition per foot of thickness will be many times greater than the rate of denudation.
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WALLACE, A. The Age of the Earth. Nature 51, 607 (1895). https://doi.org/10.1038/051607a0
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DOI: https://doi.org/10.1038/051607a0
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