Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

April, 1836. coral formations. 569 germs could be disseminated, the problem is rendered far more intelligible. Again, if the theory should hereafter be so far estabhshed, as to allow us to pronounce that certain districts fall within areas either of elevation or subsidencej'it will directly bear upon that most mysterious question, whether the series of organized beings pecuhar to some isolated points, are the last remnants of a former population, or the first creatures of a new one springing into existence. Briefly to recapitulate. In the first place, reefs are formed around islands, or on the coast of the mainland, at that limited depth at which the efficient classes of zoophytes can live; and where the sea is shallow, irregular patches may likewise be produced. Afterwards from the eff"ects of a series of small subsidences, encircling reefs, grand barriers, or lagoon islands, are mere modifications of one necessary result. Se- condly, it can be shown on the above views, that the inter- tropical ocean, throughout more than a hemisphere, may be divided into linear and parallel bands, of which the alternate ones have undergone, within a recent period, the opposite movements of elevation and subsidence. Thirdly, that the points of eruption seem invariably to fall within areas sub- ject to a propulsion from below. The traveller who is an eyewitness of some great and overwhelming earthquake, at one moment of time loses aU former associations of the land being the type of sohdity, so will the geologist, if he believe in these oscillations of level (the deeply-seated origin of which is betrayed by their forms and vast dimensions), perhaps be more deeply impressed with the never-ceasing mutability of the crust of this our World.