63 



about forty or fifty feet occurs between these columns, w 

 space is occupied by tlic jiinorphous variety elevated to s 

 jight against (hem, their edges in this case are 



ird, the effect produced upon it 



the fragments arc angular with an imperfect conchoidal fracture : 

 Its structure is coarsely granular and uneven, and is composed es- 

 sentially of hornblende, feldspar, and a greenish substance in 

 grains much resembling epidote : crystals of leucite of a yellow 

 and reddish tinge are disseminated throughout the mass whose frac- 

 tured surfaces strongly reflect the rays of light to the eye : in some 



Veins of quartz frefiuently traverse the fine variety, some of them 

 containing beautiful amethysts. 



The basis rock of these islands, as far as I could discover, is 

 the conglomerate which underlies the basalt. It is composed most 

 generally of two or three layers, about five feet in thickness each, 

 resting one on the otlier and dipping to the south east at an angle 

 of from twelve to twenty degrees. These layers are divided by 

 regular fissures into large rhombic tables, many of which appear 

 to have recently fallen out, and now lie scattered all over the slop- 

 mg sides of the hills, so that the strata when seen cropping out 

 from beneath the basalt, present a slightly arched row ol' angular 

 projections of some considerable magnitude and extent. 



These strata are chiefly composed of irregular and angular frag- 

 ments of a rock, whose principal ingredient appears to be green 

 earth, arranged with both a granular and slaty structure, united 

 by an argillaceous cement ; the whole mass when moistened by the 

 breath giving out a strong odour of that earth. The upper por- 

 tion of this conglomerate for a few feet, is of a dirty green colour, 

 and appears to be constructed by the passage of the amygdaloid 

 into this rock, the greenish fragments predominating, and they are 

 united to each other principally, by zeolite of a beautiful light red, 

 or orange colour, together with some quartz and chalcedony ; a few 

 crystals of lime cause it to effervesce slightly m some places. 

 Ihese minerals seem in a great measure to replace the earthy ce- 

 thcr, the green fragments 



