IGNEOUS ROCKS OF TASMANIA. 285 
becoming a reconstructed rock, amphibolite. _ Some beauti- 
ful amphibolites may be collected between the Heazlewood 
and Mt. Hope mines, also on the Forth River. Some of the 
dykes which traverse the Silurian slates on the Waratah- 
Corinna Road show good examples of flaser-gabbro, and 
metamorphic gabbro wich a granulated structure. 
At the mouth of the Blythe, and between Burnie and 
Cooee Creek, a gabbroid rock runs out to sea as reefs. The 
felspar is not so basic as the ordinary gabbros, and the 
pyroxene is exclusively monoclinic. It does not belong to 
the same series as our gabbros generally. It may be con- 
nected with some of the rather obscure basic rocks found 
between Mt. Bischoff and the Magnet. 
There is a very interesting group of hornblende schists at 
the Rocky and Whyte rivers, enclosing large deposits of 
magnetite, with pyrrhotite and copper ores. The area is 
one of regional metamorphism, and the schists are gabbro- 
amphibolites. Roth gave the name of Zobtenite to rocks 
which belonged geologically to the crystalline schists, and 
petrographically to gabbro; but the term has not gaimed 
general acceptance. Rosenbusch has dropped it, and now 
includes such rocks among dynamicaily-metamorphosed 
gabbros, and calls them variously flaser gabbro, gabbro 
‘schist, felspar amphibolite, amphibolite schist. Zirkel says 
that their position in the crystalline schists is such that 
there is no proof of any intrusion, and that their origin is 
bound up with the genesis of the schists. The rock at the 
Rocky River consists of green hornblende, plagioclase, 
quartz, apatite, epidote. This belt of country, with deposits 
of magnetite, extends N. 20° W. for a minimum of 14 miles, 
and is said to continue even for 25 miles. 
PERIDOTITE AND PYROXENITE. 
These ultra-basic rocks are nothing more nor less than 
felsparless modifications of gabbro, and contain ferro-mag- 
nesian minerals éxclusively. The percentages of Al and Si 
are the lowest known, the latter sinking to about 40 per 
cent. Ca Mg>s Na + K. Ca contents are more consider- 
able in pyroxenites than in peridotites, but Mg is high in 
both. Alis low. Na and K gradually disappear. The 
peridotites contain olivine; the pyroxenites are pyroxene 
rocks. In Tasmania they may be classified as under :— 
Peridotites : 
Webhrlite = dia'lage + olivine. 
Lherzolite = diallage + enstatite + olivine. 
Harzburgite = enstatite + olivine. 
