Open main menu

Page:Popular Science Monthly Volume 32.djvu/265

This page has been proofread, but needs to be validated.
253
A GREAT LESSON.

grown old in his own early convictions, was at least ready to entertain it, and to confess that serious doubts had been awakened as to the truth of his famous theory.

If, however, Mr. John Murray has not been cheered by the acclamations which greeted his illustrious predecessor, if the weight of a great accepted authority and of preconceived impressions has kept down the admiration which ought ever to reward the happy suggestions of laborious research, he has had at least the great satisfaction of observing the silence of any effective criticism. But more than this—he is now having the still greater satisfaction of receiving corroborative support from the observations of others. His own series of facts as ascertained during the voyage of the Challenger constituted an array of evidence tolerably conclusive. But since he read his paper in Edinburgh, an island has been discovered in the Solomon group by another naturalist, Dr. Guppy,[1] which lifts into the light and air a complete record of the series of operations beneath the waters of the Pacific to which Mr. Murray ascribes the origin of countless other islands, islets, and atolls. Here the barrier-reef and the atoll have been elevated from their bed, and all their foundations have been shown. Those foundations are not solid rock, but are just what Darwin assumed they could never be—deep-sea deposits. These had been originally, of course, laid down in more or less oceanic depths. But elevation, not depression, had begun the work. The deep deposit had ceased to be deep because the crust of the earth, on which it lay, had been bulged upward by subterranean force. The deep bottom had become a shoal, rising to the required distance from the surface-level of the sea. The moment it reached the thirty or the twenty fathom depth, the reef-building corals seized upon it as their resting-place, and began to grow. Possibly some process of induration may have affected the deposit before it reached this point. Probably it was consolidated or indurated by the luxuriant growth of myriads of deep-sea creatures at depths greater than thirty fathoms.

It has recently been discovered, by another naturalist of the Challenger school,[2] that there may be a special explanation of this part of the operation. It is found that shoals have the immediate effect of converting the tidal wave of deeper water into a current. This current sweeps off the looser deposits covering the shoal. Deep-sea corals then settle upon it. These may, and often do, build up their walls to a great height, and if this height reaches the zone of the true reef-building species, a firm basis is at once provided for their operations. Shoals have lately been discovered off the African coasts of the Atlantic, which in tropical seas would probably have become coral

  1. Surgeon of H. M. S. Lark. "Transactions of the Royal Society of Edinburgh," June, 1885.
  2. "On Oceanic Shoals discovered by the steamship Dacia," by J. Y. Buchanan, F. R. S. E., "Proceedings of the Royal Society of Edinburgh," October, 1883.