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lATRODUCTOKY ESSAY. 



hilly clistricl: resting almost exclusively on mineral 

 substances belonging to the clay genus. 



Upon examining the structure of the calcareous 

 formation, we find it to consist of the spoils of 

 2:oophites ; of which several species of madreporce, 

 millepora;, corallina^, and alcyonise, are strikingly 

 evident. These are cemented together by carbo- 

 nate of lime, containing an abundance, and great 

 variety, of shells. The cement may be said to vary 

 from marl, more or less indurated, to a hard com- 

 pact limestone, with conchoidal fracture, and 

 transluccncy on the edges. In some places the 

 organic remains constitute the principal, in all a 

 very considerable portion of this formation ; and 

 although these remains are intimately blended 

 the common structure, they appear to be 

 arranged in families: in some situations the 



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rnadreporcB, in others the alcyonia?, being most 

 conspicuous. This structure of the calcareous 

 formation prevails throughout its whole extent, 

 even at its highest elevation, which reaches nearly 

 eleven hundred and fifty feet ; and in sonui [)laces, 

 as in the neighbourhood of Ilackleton's Cliff, at 

 Ape's Hill Guily, and in many other simihir situa- 

 tions, mural precipices of this coralline aggregat 



are exposed, between one and two hundred feet in 

 height. Upon this coralline mass is occasionally 

 found beds of white shelly sandstone, similar to 

 that of Guaduloupe, in which the reliquiae of human 



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