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gascar than of Mauritius or Bourbon to which it ia topogra- 

 phically so much more closely adjacent, 



I have done my best to procure information as to the depth 

 of the narrow Channel which divides Round Island from our 

 shores, but regret to say there is no very reliable evidence ; 

 for, little to the Credit of either Imperial or Colonial Govern-, 

 ments, the Mariner approaching Mauritius at the present day 

 has still to trust to charts founded on the general survey of 

 Mauritius made by the Abbe de la Caille a century ago. No 

 soundings between the Islet and the Mainland are given on 

 these, save one of 25 fathoms close to the former, but the 

 Harbour Master informs me that be believes the depth to 

 vary from 30 to 40 fathoms. This is not to be compared with 

 that of the Mozambique Channel which has for many ages 

 interrupted the land communication between African and 

 Madagascar, but I am inclined to suppose it to be about the 

 average depth throughout the Mascarene Archipelago. 



If so, neither the formation, nor possible future disappear- 

 ance of that Archipelago, would seem by any means so incom- 

 prehensible as might at first be imagined ! 



It would require simply, in order to accomplish this latter 

 transformation, that the oscillating movement of laud and 

 water, should be reversed on this part of the globe's surface, 

 for a thousand years or so. At present, this island, in com- 

 mon with such of its numerous and distant dependencies as 

 are surrounded by reefs of living coral, is supposed to be 

 sinking slowly, at such a rate as to enable these Insects to 

 continue to rear their fabric to the level of the Ocean, with- 

 out working out of water, which would be speedy destruction 

 to them. It is however clearly apparent from the elevated 

 beds of extinct corals to be found, often a considerable dis- 

 tant inland, that this was not always the case, but that at 

 former periods, the land had risen to such an extent, that 

 reefs have become dry, and the polypes have perished. 



I have been assured that masses of these imbedded corals, 

 are to be seen at the height of many hundred feet, on the 

 road up to the Charaarel Falls, for example. I have myself 

 extracted existing species from the very top of the bluff of 

 volcaaic rock, three hundred feet high, oa which the £^lafi 



