114 Lieut. Nelson on the Geology of the Bermudas. 



The last individual Animal Organic which I shall mention, is a Strombus which I chiselled out at 

 Long-bird Island, and had the cavities in the substance of the shell filled with crystallized car- 

 bonate of lime. I may terminate this list comprehensively by saying, that almost every shell now 

 known in the surrounding sea, may be found in the rock quite perfect, except with regard to 

 colour, especially among the newer beds on the sea coast. 



Chalk. — It may be considered rather a bold step to place this mineral un- 

 der the head of ' Organics/ but from all that I have seen during different 

 examinations of decomposing zoophytes and shells, from the least calcareous 

 to the large and massive Mseandrina and Astrea, not only whilst breaking 

 or cutting them with my own hands, but as obtained from the extensive ex- 

 cavations made by the dockyard diving-bells for the foundations of the wharfs, 

 and from the soil torn up by large mooring anchors, 1 have no more hesitation 

 in attributing the existence of the Bermuda chalk to such a source, than 1 

 have for asserting that the obvious material of the Bermuda stone is derived 

 from the same origin ; with, however, this difference, that in the latter 

 instance the fragments are the result of mechanical subdivision ; while in 

 the former, the elementary particles are due to the decay, by long submer- 

 sion, of the membranous tissue*, which, pervading their whole structure, 

 releases the constituent calcareous matter dispersed through the texture, when 

 it is ruined by decomposition. These animals, and the many marine plants, 

 consisting chiefly of lime, produce this chalk, just as terrestrial animals and 

 vegetables give carbon to soil when they decay. I no more pretend to argue 

 that the European chalk was thus produced, than that the caverns of all the 

 various limestones were formed by means similar to those which excavated the 

 caves at Bermuda (see page 119); or that the coral rag of the oolites is related 

 to that of the North Bastion ; but certainly the external and the chemical 

 peculiarities are as much the same as their common character of being marine 

 deposits. 



This chalk, as found in the harbour bottom, is much mixed with shell-sand, corals of many 

 sorts, shells in a perfect state, and gigantic masses of equally perfect Astrea and Mceandrina, as 

 well as in every stage of decay, leaving no doubt of their having lived and perished where they 

 are found. The aspect of this chalk when fresh, is precisely that of crude mortar. A variety, 

 which may be termed stalactitic, was found in some of the newly opened caves, and resembled 

 curds in consistency! . In some cases it occurs in small shapeless deposits among the regular 

 strata, or lining the crevices and insides of caverns. This variety, when dry, consists of very 

 fine white powder, which yields to the least pressure and soils the fingers. 



* When a fresh specimen of any sort of coral is carefully submitted to very diluted muriatic 

 acid, the membranous tissue may be obtained as satisfactorily as from a bone. 



t The same substance is to be found on the lower surface of the crust covering the bottom of 

 Chudleigh rock caverns. 



