Geology.} 
NATURAL HISTORY. 
607 
very nearly resembling specimens from the trap rocks* of 
the Wrekin and Breeden Hills in Shropshire. Reddish and 
yellowish sandy clay^ coloured by oxide of iron, and used 
as pigments by the natives. 
Percy Islands, about one hundred and forty miles north 
of Cape Capricorn . — Compact felspar of a flesh-red hue, 
enclosing a few small crystals of reddish felspar and of 
quartz. — This specimen is marked “ general character of the 
rocks at Percy Island,” and very much resembles the com- 
pact felspar of the Pentland Hills near Edinburgh, and of 
Saxony. Coarse porphyritic conglomerate, of a reddish hue. 
Serpentine. A trap-like compound, with somewhat the as* 
pect of serpentine, but yielding with difficulty to the knife. 
— This specimen has, at first sight, the appearance of a con- 
glomerate, made up of portions of different hues, purplish, 
brown, and green; but the coloured parts are not other- 
wise distinguishable in the fracture : — It very strongly re- 
sembles a rock which occurs in the trap -formation, near 
Lyd-Hole, at Pont-y-Pool, in Shropshire. Slaty clay, with 
particles of mica, like that which frequently occurs imme- 
diately beneath beds of coal. 
* By the terms Trap, and Trap formation, which I am aware 
are extremely vague, I intend merely to signify a class of rocks, 
including several members, which differ from each other consider- 
ably in mineralogical character, but agree in some of their prin- 
cipal geological relations ; and the origin of which very numerous 
phenomena concur in referring to some modification of volcanic 
agency. The term Greenstone also is of very loose application, 
and includes rocks that exhibit a wide range of characters ; — 
the predominant colour being some shade of green, the structure 
more or less crystalline, and the chief ingredients supposed to 
be hornblende and felspar, — ^but the components, if they could be 
accurately determined, probably more numerous and varied, than 
systematic lists imply. 
