234 APPENDIX. 



Chagos, Maldiva, and Laccadive Archipelagoes. — 

 These three great groups which have already been often 

 noticed, are now well known from the admirable surveys 

 of Capt. Moresby and Lieut. Powell. The published charts, 

 which are worthy of the most attentive examination, at 

 once show that the Chagos and Maldiva groups are entirely 

 formed of great atolls, or lagoon-formed reefs, surmounted 

 by islets. In the Laccadive group, this structure is less 

 evident ; the islets are low, not exceeding the usual height 

 of coral formations (see Lieut. Wood's account, Geograph. 

 Journ., vol. vi. p. 29), and most of the reefs are circular, as 

 may be seen in the published charts ; and within several of 

 them, as I am informed by Capt. Moresby, there is deepish 

 water; these, therefore, have been coloured blue. Directly 

 north, and almost forming part of this group, there is a long, 

 narrow, slightly curved bank, rising out of the depths of the 

 ocean, composed of sand, shells, and decayed coral, with 

 from twenty-three to thirty fathoms on it. I have no doubt 

 that it has had the same origin with the other Laccadive 

 banks ; but as it does not deepen towards the centre I have 

 not coloured it. I might have referred to other authorities 

 regarding these three archipelagoes ; but after the publica- 

 tion of the charts by Capt. Moresby, to whose personal 

 kindness in giving me much information I am exceedingly 

 indebted, it would have been superfluous. 



Sahia dc Maiha bank consists of a series of narrow banks, 

 with from 8 to 16 fathoms on them ; they are arranged in a 

 semicircular manner, round a space about forty fathoms 

 deep, which slopes on the S.E. quarter to unfathomable 

 depths ; they are steep-to on both sides, but more especially 

 on the ocean-side. Hence this bank closely resembles in 

 structure, and I may add from Capt. Moresby's information 

 in composition, the Pitt's Bank in the Chagos group ; and 



