140 GEOLOGY OF THE WEST INDIES. [Nor. 



hornbiend, with feldspar imbedded in it, forms the prin- 

 cipal part of these rocks, which vary in colour, from nearly- 

 black to gray, the feldspar being generally crystallized, 

 and frequently diaphanous, passing through the porous or 

 scorious rocks without indications of having undergone 

 much chaage. There are two principal modes by which 

 the production of cinders or ashes may be accounted for: 

 they muy be thrown from the crater of a volcano during 

 an irruption of lava, and in that case they consist of small 

 pieces of scoria, pumice, &c. and are placed in strata of 

 various thicknesses and colours, as if deposited by water; 

 or they may be ejected from volcanoes nearly exhausted, 

 mixed with water and rocks, forming large beds or cur- 

 rents, of an agregate, which is in time cemented, and wears 

 the appearance of a brechia. A third mode is, perhaps, the 

 irruption of lava into the sea, at the commencement of 

 submarine volcanoes, when by means of the sudden cool- 

 ing, the melted lava might crumble into small angular 

 sand, and form beds of cinders. From Kingston to the 

 north end of the island, the same alternation of cinders 

 and solid lava obtains, forming steep precipices, and nar- 

 row vallies, the wearing and excavation of which, by the 

 mountain torrents, is facilitated by the prevalence of the 

 cinders, which increases as you approach the Soiifriere^ a 

 name given, in the West Indies, to spots which indicate 

 the remains of a subsiding volcano, and whence hot sul- 

 phureous vapours are ejected throu^ fumerols^ depositing 

 sulphur, and bleaching the surrounding rocks into alum- 

 stone, as at Solfa-terra near Naples. 



The fumerols of this Soufriere are at present extinguish- 

 f;d, perhaps by the last irruption of cinders in 1812, when 

 the crater threw a mixture of water, rocks and cinders, 



