The Voyage Of The Beagle By Charles Darwin





































































 -   On the
other hand, although most of the islands in the Pacific which
are encircled by barrier-reefs, are of - Page 382
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On The Other Hand, Although Most Of The Islands In The Pacific Which Are Encircled By Barrier-Reefs, Are Of Volcanic Origin, Often With The Remnants Of Craters Still Distinguishable, Not One Of Them Is Known To Have Ever Been In Eruption.

Hence in these cases it would appear, that volcanos burst forth into action and become extinguished on the same spots, accordingly as elevatory or subsiding movements prevail there.

Numberless facts could be adduced to prove that upraised organic remains are common wherever there are active volcanos; but until it could be shown that in areas of subsidence, volcanos were either absent or inactive, the inference, however probable in itself, that their distribution depended on the rising or falling of the earth's surface, would have been hazardous. But now, I think, we may freely admit this important deduction.

Taking a final view of the map, and bearing in mind the statements made with respect to the upraised organic remains, we must feel astonished at the vastness of the areas, which have suffered changes in level either downwards or upwards, within a period not geologically remote. It would appear also, that the elevatory and subsiding movements follow nearly the same laws. Throughout the spaces interspersed with atolls, where not a single peak of high land has been left above the level of the sea, the sinking must have been immense in amount. The sinking, moreover, whether continuous, or recurrent with intervals sufficiently long for the corals again to bring up their living edifices to the surface, must necessarily have been extremely slow. This conclusion is probably the most important one which can be deduced from the study of coral formations; - and it is one which it is difficult to imagine how otherwise could ever have been arrived at. Nor can I quite pass over the probability of the former existence of large archipelagoes of lofty islands, where now only rings of coral-rock scarcely break the open expanse of the sea, throwing some light on the distribution of the inhabitants of the other high islands, now left standing so immensely remote from each other in the midst of the great oceans. The reef-constructing corals have indeed reared and preserved wonderful memorials of the subterranean oscillations of level; we see in each barrier-reef a proof that the land has there subsided, and in each atoll a monument over an island now lost. We may thus, like unto a geologist who had lived his ten thousand years and kept a record of the passing changes, gain some insight into the great system by which the surface of this globe has been broken up, and land and water interchanged.

[1] These Plants are described in the Annals of Nat. Hist., vol. i., 1838, p. 337.

[2] Holman's Travels, vol. iv. p. 378.

[3] Kotzebue's First Voyage, vol. iii. p. 155.

[4] The thirteen species belong to the following orders: - In the Coleoptera, a minute Elater; Orthoptera, a Gryllus and a Blatta; Hemiptera, one species; Homoptera, two; Neuroptera a Chrysopa; Hymenoptera, two ants; Lepidoptera nocturna, a Diopaea, and a Pterophorus (?); Diptera, two species.

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