192 THE ANTARCTIC MANUAL. 
if of aqueous origin, may be searched for fossils ; in all cases, how- 
ever, they trequently exhibit signs of having undergone changes by 
the action of heat, acid vapours, etc. upon them. Such masses should 
be broken up and carefully examined, for they frequently enclose in 
their cavities some of the most beautifully crystallised varieties 
known to the mineralogist. 
The general instructions as to the instruments best adapted for 
the purpose of the geological observer, and of the tools used for 
obtaining rock specimens and minerals, are of course equally appli- 
cable to the student of vuleanology. But as igneous rocks are in 
many cases especially liable to change by weathering, the greatest 
efforts should be made to obtain specimens as fresh and little altered 
as possible. In those cases, however, where the rock assumes any 
peculiar features in consequence of meteoric actions upon it, speci- 
mens both of the unaltered and of the altered rock are desirable. 
Works of reference on Vulcanology, useful to the traveller :— 
G. Poulett Scrope, Volcanoes. 2nd edition. 1572. Longman & Co. 
J. W. Judd, Volcanoes: what they are, and what they teach. 1881. Kegan Paul 
Tribner & Co. 
T. G. Bonney, Volcanoes: their Structure and their Significance. 1899. John 
Murray. 
