DR. GUPPY'S letter shows that I have not been sufficiently explicit on the subject of the formation of atolls, yet I cannot well understand that I have been obscure on the subject of his first question. Surely it is a sufficient reason for rejecting the theory of subsidence as applied to the Chagos Group that I fancy myself, in conjunction with M. Spurs, to have detected evidences of elevation in Diego Garcia. Darwin laid great stress on the character of the Great Chagos Bank as affording evidence of his theory of subsidence; he considers it to be an atoll drowned by a too rapid act of subsidence; but, as I have pointed out, if this were so it is impossible to understand how two atolls such as the Great Chagos Bank and Centurion's Bank could have been thus destroyed without Six Islands or Egmont's Atoll, which lies directly between them, being involved in their destruction. Further, the raised atolls north of Madagascar are unquestionable proofs of upheaval in this region, yet in the same region are low-lying atolls, atoll-shaped reefs awash, and submerged atoll-shaped banks. Clearly the theory of subsidence does not apply to these groups, and I do not see any reason for supposing that the Laccadive and Maldive Islands have been formed differently to the other atolls in the Indian Ocean, though I am unable to bring forward any fresh arguments with regard to them.
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BOURNE, G. “Coral Formations”. Nature 38, 5 (1888). https://doi.org/10.1038/038005c0