"i 
55 
disintegration of a compact and apparently pure opal rock 
was an unexpected occurrence. n examination it was found 
that an efflorescence of salt covered all the planes of fracture, 
7s this is suggestive of the cause of the disintegration. The 
ect : : 
retained its quarry-water, or "sap-water," to use a quarry- 
man's term, but when placed in the cabinet desiccation 
This action is known to be operative in all dry regions 
where the surface waters are mostly mineral solutions and 
motel to alternate conditions of imbibition and desiccation. 
ally those of an open texture, such as sandstones, shales, clays, 
etc., many examples of such chemico-mechanical disintegration 
were noted in the region referred to. 
IV. NopuLAR BARYTES or PECULIAR FORMS FROM 
CENTRAL AUSTRALIA. 
Barytes (barium sulphate), or ''heavy spar," occurs in 
South Australia under a varist of forms. In Mitcham 
orthorhombic crystals, and also of lamellar structure and 
translucen 
occurs in veins with a granular crystallization, as in the 
gangue in mineral lodes, as at the New Burra Copper Mine, 
oori 
all uncommon. Some of these have mammillary forms, white 
to brownish in colour, columnar and radial in structure, with 
rm liquid had been poured out of some vessel—weighs 
