104 Lieut. Nelson on the Geology of the Bermudas. 



resemblance to the Otdia, or RomanzofF islands. The principal islands are 

 generally separated by channels, from ten to twenty feet deep, and many of 

 the spaces between the smaller islands are fordable. The depth within the 

 reef rarely exceeds twelve or fourteen fathoms*. 



The highest land is at Sear's Hill, immediately above and to the westward 

 of Harrington Sound. Its summit may be about 260 feet above the sea ; that 

 of Gibbs' Hill is 245 feet. These and all the other numerous small emi- 

 nences, have much the appearance of sand hills in shape, and chalk downs in 

 colour. 



The whole of the islands are composed of calcareous rocks, derived from 

 comminuted shells and corals; and vary in texture from loose sand to a hard 

 compact limestone, susceptible of a good polish. The varieties are irregu- 

 larly associated, and without any order of superposition f. 



From the saddle-shaped sections observable throughout the islands, the 

 strata have evidently been accumulated round numerous and contiguous 

 centres : the question as to the agency to which this is attributable, will be 

 discussed in its proper place {. 



The bottom of the basin consists of coral reefs (which do not appear above 

 low water mark, except at spring tides) and calcareous sand, the last being 

 associated with considerable tracts of chalky ground, in which the best an- 

 chorages are found. I have met with this chalk likewise as a constituent of 

 the rock, lying irregularly among its beds in a soft state, or lining caverns, 



* Kotzebue describes the coral islands of the Pacific as consisting of circles of islets, amounting 

 in some instances to sixty, and surrounding a lagoon. The intervals between the islets are dry at 

 ebb tide ; but the centre of the lagoon generally varies in depth from thirty to thirty-five 

 fathoms, the soundings gradually decreasing towards the margin. In those seas, where the con- 

 stant monsoons prevail, the windward side of the island first rises above the level of the water, 

 being composed chiefly of blocks of coral and fragments of shells thrown up by the waves. 

 Voyage to Behring's Straits, vol. iii. p. 333 : 1821. 



In Kotzebue's chart of the Radack and Ralick chains, there are exceptions to the rule of the 

 islands being exactly on the windward side. Bermuda is not subject to any very regular wind ; 

 perhaps more to the south-west than any other. Currents have been likewise observed setting 

 towards the island from the north-east, though I cannot say whether permanently or not ; or 

 whether the gulf stream possesses any influence in those parts. The harbours at Bermuda are 

 not always so particularly ' calm'; and it is only in certain points that they are absolutely ' secure'. 



There are several entrances to the interior practicable to vessels of about twelve feet water ; 

 but only two for ships of any size, the south-east passage, and that of the north rock, both very 

 intricate. 



t See Kotzebue's similar account of the structure of coral islands. Ibid. vol. ii. p. 357 ; 

 vol. iii. p. 1 4 1 ; and in particular the alternation of beds of sand and limestone. Ibid. pp. 1 44, 1 45. 



J See Kotzebue, vol. iii. p. 144, for similar conformations in the strata. 



