and Volcanic Substances. 231 
Analysis of common Hornblende. —Augit (Frascati.) 
Silex - ~ 42 48 
Alumine - - 12 5 
Lime - . 11 24 
Magnesia - - 2 25 8 75 
Oxyd of Iron - 30 12 
Manganese - 25 1 
ater - 
Trace of potash - 
The black some wherein either hornblende or augit 
predominates, do not decompose e action of air and 
moisture so easily as Bitte greyish trachytic varieties which 
contain more felspar. The olivine or peridot of the cellu- 
lar basalt, also decomposes easily into an ochreous pow- 
der ong exposure, all kinds of basalt gradually de- 
compose into a yellowish fertile soil. Terras or Puzzuolana 
basalt, containing much iron: and argillaceous iron ores 
have been found of nee value for like purposes. 
asalt Lavas, and Basalt floetz trap, moreover agree in 
an Sale. noticed by M. Conybeare, 3 Geol. trans. 
The newest formations are the lowest—the least ele- 
foot of mountains : bu » an - vom 
and basalts are found covering high mountains as in Sax 
and other parts of Germany, and in South-America. 
Among the decided volcanic formations, the least an- 
cient, are the “ni elevated ; but the flceetz trap surmounts 
all others. Of all other formations, the degree of consoli- 
dation decreases, as they are of later origin : thus the most 
crystalline are the primitive: next come the transition 
which are sub-crystalline ; ; then the compact, coarse, and 
earthy : while in the fletz trap, even where it rests on 
ri the crystalline character of the older rocks often ap- 
pear 
Whin-Dykes which belong to the fleetz trap basalt, and 
amygdaloid, differ from all other mineral veins, by travers- 
ing all rocks indifferently as Lava does; while other mine- 
ral veins are associated with particular rocks. 
