Geology, ancient Jirts, &e.  _ 245 
The second part of the 5th Vol. cf the Transactions of 
the Geological Seeiety of London is announced to be pub- 
lished ‘‘ early in October.” 
Dr. Macculloch has given the name Chloropheite to a 
mineral found in Fife and Rum, (Scotland,) and which has 
been since feund in Iceland,.in an amygdaloidal rock. It 
has the singular property “of being perfectly transparent, 
and of a bottle-green colour, when taken out of the rock, but 
becomes opaque when removed from its place, or exposed 
to the air.” From the observations of Dr. Brewster, it ap- 
pears that this change is a mechanical one. ‘ ‘The cause 
of ithis change may. be conceived,” observes Dr. Brewster, 
“* by supposing a number of prisms assembled in a particular 
manner and kept together by screws, so as to bring their 
touching surfaces into that. close contact which prevents total 
reflection at the junctions. The mass of aggregated prisms 
willbe now quite transparent; but if we either diminish the 
“compressing forces by loosening the screws, or suppose 
some force similar to the disintegrating force of the atmos- 
~ phere, to-act.in opposition, to the cohesive force represen- 
ted by the action.of the screws, the touching surfaces will be 
separated, and the whole mass become opaque.” 
Edinburgh Philosophical Journal, No. 8. 
oo Dre Fyfe, (of. Edinburgh,) has analysed the Hydrate of © 
» Magnesia from Hoboken, and found it to consist of 68.57 of 
Magnesia, and 31.43. of Water, with a trace of Lime. "The 
same gentleman examined the Hydrate of Magnesia discov- 
‘ered by Dr. Hibbert in Ust, one of the Shetland Islands, 
see found it to consist. of Magnesia 69. 13, Water 30.25. 
Heuer. ‘No 9 of the Edinburgh Pilesbptsved Journal. 
“ New System. of Mineralogy. —Dr. Brewster is preparing 
for the press a Treatise on Mineralogy, founded chiefly on 
the physical relations of mineral bodies, and embracing an 
-account of those remarkable phenomena which have been 
detected in crystallized substances by the. agency of com- 
mon and polarised light. {n this work the unerring charac- 
-ters which are derived {rom optical structure will be substi- 
tuted in place of the ambiguous distinctions which have been 
senerally employed; and the student will be pied jo a 
Vou. TEH......No. 2. 6 
