N 





INTRODUCTORY ESSAY. 



7 



bodies have recently been discovered. This sand- 

 stone is quarried for the purposes of building, and, 

 being sufficiently porous, is employed for the filtra- 

 tion of water. It sometimes seems disposed to 

 assume the slaty structure, and when the beds are 

 of considerable thickness they simulate the appear- 

 ance of stratification. Calcareous spar also, and 

 calc sinter, occur abundantly; and I have seen small 

 specimens of wliite granular limestone. These are 

 found attached to the common calcareous rock, 

 and, like the spar, have been deposited in acci- 

 dental cavities at a comparatively recent period. 



The whole of the calcareous portion of the island 

 presents numerous rents and fissures j the smaller 

 are filled with chrystallized and other modilications 

 of carbonate of lime j the larger remain open, and 

 are the deep precipitous ravines, or gullies, whicli 

 are so very frequent in the higher parts of this 

 district, and whicli beconio during the rainy season 

 the conducting clianrK^ls of temporary torrents- 

 This calcareous formation is extremely cavernous; 

 dislocations, and sniking of the surface, occasionally 

 take place at tiie present time, and from general 

 appearances, we must conclude tluit they happened 

 very frequently, and to a considerable extent, at 

 former periods. It is to this cause that the island 

 is plentifully supplied with fissures, through which 

 the water lodged on the surface is drawn off, 

 a])d conducted to the ocean by means of subter- 



::^ 





t- 



u 



■ii: 



■M 



