Geology, ancient Arts, &c. 245 
The second part of the 5th Vol. cf the Transactions of 
the Geological Society of London is announced to be pu 
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 found in Iceland, in an amygdaloidal rock. It 
has the singular property “ of being parfoetty 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 Soe ee one. “ The catse 
of this change may be conceived,” observes Dr. Brewster, 
* by supposing a number of iiss 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 
will be 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 Hy whole mass become opaque 
Edinburgh Philosophical Journal, No. 8. 
Dr. Fyfe, (of Edinburgh,) has analysed the Hydrate of 
Magnesia from Hoboken, and found it to consist of 68.57 of 
Mepnent, and 31.43 of Water, with a trace of I Lime. The 
same gentleman examined the Hydrate of Magnesia discov- 
ered by Dr. Hibbert in Ust, one of the Shetland een 
and found it to consist of Magnesia 69.75, Water 30.25 
mon and ‘pales jek In this work the unerring charac- 
ters which are derived from optical structure will be substi- 
tuted in place of the ambiguous distinctions which have been 
g gy ae ae and the — will be allured to a 
4 
