212 Notices of the Geology and Mineralogy of Sicily. 
¥arious minerals,which are all derived from primitive rocks. 
—These are ; 1. Feldspar, the most abundant, varying in 
size from minute threads and scales to distinct prisms and 
tables.—In some lavas of the middle age they form more 
than a third of the mass. 2. Black Pyrowene, equally 
abundant, entire, or in fragments. —3. Chrysolite (olivine) | 
green or reddish ; the latter colour probably from the more 
violent action of heat, as they are of a deep red in the 
porous lavas and scoria.—Abbe F. thinks they ought 
rather to be considered as red quartz. Jn many lavas, par- 
ticularly in the great current of Licatia, near Catania, there 
are large distinct crystals of Chrysolite of a beautiful green, 
6 lines long, in regular 4 sided prisms, and very brilliant.— 
When exposed to greater heat or decomposition by water, 
they are ferruginous. They are easily detached from the 
lavas, which is not the case with the minute grains,whence 
Prof. F. concludes that they were only involved by the 
lavas, but net of coeval formation like the latter. In the 
currents near Paterno, there are yellow and black scales of 
Mica, No Leucite is mentioned by Prof.F. as occurring in 
the lavas of /Mtna. These crystals preserve their form 
and brilliance perfectly in the compact lavas but are more 
or less altered in the porous. ‘The lavas of all ages are 
either compact or porous, owing to the different degrees of 
heat to which they were exposed ;, varying in this respect 
from the most compact trap-like lava to the lightest 
pumice, and even passing from one to the other on the same 
specimens. Scoria, sand, and ashes are al! formed of the 
same paste with the most compact lavas, only altered by 
the greater degree of heat or mechanical violence—Com- 
pact lavas are easily compared with the analogous miner- 
als unaltered by fire. The crystals in the lavas are looser, 
the feldspar in the porphyritic lavas 1s more distinct in its 
outlines, less brilliant and drier. The lavas are also more 
sonorous, fusible and magnetic. In the ancient lavas near 
Palagonia, there are masses of Black Glass, (Obsidian) for- 
med, says Prof. F. of a fine grained petrosilex. Abbe F. 
found on the surface of the lava of 1792,a mass of fine grain- 
ed earthy petrosilex traversed by a vein resembling flint. 
Some of the more simple lavas resemble the trap, &c., in 
ihe mountains of Pelorus.—The finest kinds of compound 
