Ci;oLUGV Ul' I'UKTU I'K.WA. 7 



ca, and at points sixteen liundred miles distant in 

 a north and south direction. In some dust which 

 was collected on a vessel three hundred miles from 

 the land, I was much surprised to find particles of 

 stone above the thousandth of an inch square, mix- 

 ed with finer matter. After this fact one need not 

 be surprised at the diffusion of the far lighter and 

 smaller sporules of cryptogamic plants. 



The geology of this island is the most interesting 

 part of its natural history. On entering the har- 

 bour, a perfectly horizontal white band in the face 

 of the sea cliff may be seen running for some miles 

 along the coast, and at the height of about forty- 

 five feet above the water. Upon examination, this 

 white stratum is found to consist of calcareous mat- 

 ter, with numerous shells embedded, most or all of 

 which now exist on the neighbouring coast. It 

 rests on ancient volcanic rocks, and has been cov- 

 ered by a stream of basalt, which must have en- 

 tered the sea when the white shelly bed was lying 

 at the bottom. It is interesting to trace the changes 

 produced by the heat of the overlying lava on the 

 friable mass, which in parts has been converted 

 into a crystalline limestone, and in other parts into 

 a compact spotted stone. Where the lime has 

 been caught up by the scoriaceous fragments of the 

 lower surface of the stream, it is converted into 

 groups of beautifully radiated fibres resembling 

 arragonite. The beds of lava rise in successive 

 gently-sloping plains, towards the interior, whence 

 the deluges of melted stone have originally pro- 

 ceeded. Within historical times, no signs of vol- 

 canic activity have, I believe, been manifested in 

 any part of St. Jago. Even the form of a crater 

 can but rarely be discovered on the summits of the 

 many red cindery hills ; yet the more recent streains 

 can be distinguished on the coast, forming lines of 



