ROCK SPECIMENS. 
cclvii 
stripes like the onyx from Iceland and Ferroc ; fragments of red jasper, and 
of a jaspery breccia ; a piece of a compact hornstone-like mass of greenish 
colour mixed with reddish, and small rolled pieces of basalt. There is 
also among them a specimen of wood-hornstone of greyish-brown colour, with 
concentric yellowish-white rings. Nor should I omit mentioning a similar 
specimen of woodstone from Byam Martin’s Island, with numerous close con- 
centric rings, the curve of which indicates its being a fragment of the stem 
of a petrified dicotyledonous tree. It is susceptible of taking a beautiful 
polish. 
