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

568 CORAL FORMATIONS. April, 1836. of elevation, but that we possessed no means of knowing it. I conceive it is by eliminating this source of doubt, that the alternate bands of opposite movement, deduced from the configuration of the reefs, directly bear on this law. I need not do more than simply state, that we thus obtain (if the view is correct) a means of forming some judgment of the prevailing movements, during the formation of even the oldest series, where volcanic rocks occur interstratified with sedi- mentary deposits. Any thing which throws Ught on the movements of the ground is well worthy of consideration ; and the history of coral reefs may, in another manner, elucidate such changes in the older formations. As there is every reason to believe that the lamelliform corals grow only abundantly at a small depth, we may feel sure, where a great thickness of coral limestone occurs, that the reefs on which the zoophytes flourished, must have been sinking. Until we are enabled to judge by some means what were the prevailing movements at different epochs, it will scarcely ever be possible to speculate with any safety on the circumstances under which the complicated European formations, composed of such different materials and in such different states, were accumulated. Nor can I quite pass over the probabihty of the above views illustrating those admirable laws first brought forward by Mr. Lyell, — of the geographical distribution of plants and animals, as consequent on geological changes. M. Lesson has remarked on the singular uniformity* of the Indio-Poly- nesian Flora throughout the immense area of the Pacific ; the dispersion of forms having been directed against the course of the trade-wind. If we believe that lagoon islands, those monuments raised by infinite numbers of minute architects, record the former existence of an archipelago or continent in the central part of Polynesia, whence the * Perhaps this is stated rather too strongly ; but M. Lesson, of course, had grounds for his assertion.