Page:Popular Science Monthly Volume 41.djvu/417

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THE following letter, respecting a former article in the Monthly, has been addressed to the Editor:

Editor Popular Science Monthly:
Does M. A. de L'Apparent's interesting address[1] on The Future of the Dry Land exhaust all the factors of the inquiry? Is it certain, for example, that some at least of the greatest mountain-chains have not in the main risen in elevation faster than the eroding agencies have depressed them? Are not some of them, and those now among the boldest, admitted to have been uplifted in comparatively recent times, geologically speaking—more recently, for example, than the advent of some of the rivers which intersect them? Erosion must have commenced from the very beginning of the upheaval and have continued to the present time; yet they grew in stature in spite of it, for no one now supposes that the upheaval was a sudden one. Indeed, the persistence of the river's "right of way" proves both the constant action of "the elements" and the extremely gradual character of the upheaval. If our planet, as some think, continues to slowly contract from a once nebulous condition, its advancing age might be expected to be marked by wrinkles, just as we know it to be.

Again, is there not good ground for the conjecture that our globe, however slowly, is approaching a state of desiccation such as is manifested partially in our neighbor Mars and still more notably in the moon?[2] Is there not some lingering continuance of the once active absorption? Is there not, for example, reason to believe that the proportion of sea area has in the main steadily diminished and that upheaval of the land masses has steadily increased since Silurian times?

To the lay reader this masterful and interesting paper of the French savant seems a courteous invitation to one of his compeers to take up the thread of his discourse at the point at which he elects to leave it.George Henry Knight.

Temple Court, New York.

Other letters on this subject have been received, all of which indicate that the matter has attracted more interest than was anticipated. Our correspondents may find on closer examination of M. de L'Apparent's paper that he avowedly presents it as covering only one side of the question, and that, while he does not discuss

  1. Popular Science Monthly, June, 1891.
  2. Do not northern Africa and western Asia contain vast regions that have passed from exuberant fertility to hopeless aridity even during the historical period?—G. H. K.