26 PRELIMINARY INQUIRIES. 



event would bring all the foundations of these reefs to the surface, each bearing its narrow, loft_v, 

 Ijerpendicular-cliffed coral tower, circled ^vith precipices such as it has not entered into the mind of 

 man to conceive, whose height is not to be reckoned by feet, biit by miles ; where the light of day 

 would scarcely penetrate to the bottom of the deej) channels between those which stood near each 

 other ; and with the top of each, all on one level, like mighty shot-towers or bastilles. Each has no 

 doubt been formed as the elevations on which they stand successively sank beneath the sea. ■ Some, 

 no doubt, may be founded on ordinary hills or even lofty mountains, when we shoidd liave, on a 

 colossal scale, a curious i-esemblance to the round j^illars or towers on hill-tops, with which it is 

 the fashion of Englishmen in their different coxmties to preserve the memory of their great men. 



Some indeed have thought, that the atolls and reefs might be the indications of the highest 

 peaks of ranges of moimtains. But tliis idea seems inconsistent with their j^osition as well as 

 tlieir composition. Their general distribution indicates ratlier the beaconing of each elevation, small 

 or great, as it successively sunk beneath the level of the ocean. Mr. Darwin objects to the idea 

 on the ground that oceanic islands, where rock is found, are almost universally composed of volcanic 

 minerals. If they had originally existed as mountain ranges on the land, some at least of the 

 islands would have been formed like other movmtain summits of granite, metaniorphic schists, old 

 fossiliferous, or other such rocks, instead of consisting of mere piles of volcanic matter.* The 

 irregidar distribution of many of the atolls and reefs, moreover, is opposed to the idea of their 

 being parts of mountain ranges, and the long lines of others may be better reconciled with 

 barrier reefs along the lines of coast than chains of moimtains, when the subsidence began. Every 

 little eminence a few feet high would furnish as good a foimdation and starting-point for the 

 coral architects as the serrated peaks of the loftiest mountains. 



The facts proved by Mr. Darwin, however, aR relate to the past. It is quite consistent with 

 them that the subsidence which they prove may now have ceased, and that as contended for by M. de 

 Ilochas, an elevatory movement may have commenced. We know that there has been an eleva- 

 tory movement subsequent to the depression, both on the shores of Africa and in India, and the 

 Indian Archijjelago. M. de Rochas maintains that no coral island can have been raised above the 

 water by the agency to which their rise is usually ascribed, viz. by a deposit from the waves dash- 

 ing over the reef, and that the only means by which they can have appeared is by an upheaval, 

 pushing them up from below. He has insjoected coral islands in various parts of the globe, and 

 finds the surface free from the attrition and fractures which ought to result from the throwing over 

 them of ijcbbles and sand by the waves ; and he also finds the coral in many places where no 

 upheaval has raised it above the surface, remaining in j)recisely the same position in which it was 

 observed long ago, with no accumulation of debris at its surface. It does not concern us much 

 to determine which is the true explanation. The fact of subsidences and elevations having taken 

 place at certain places and in a certain order, is what we chiefly require to make sure of. 



We have no data to determine witli anything like accuracy to what extent these subsidences 

 have taken place. We cannot even tell In some which are believed to be rising, whether they have 

 only just begun to do so, or if they have for a long time changed from subsidence to elevation. It 

 would seem as if nothing could be easier than to do this, because the raised clifis of coral along the 

 sea-shore should speak for themselves. Biit Mr. Darwin has shown, that in the natural course of 

 things it is not probable that coral reefs elevated by a gradual rise of the land would often be 



* Darwin"s " Origin of Species," 3rd edit., p. 388. 



