IGNEOUS ROCKS OF TASMANIA. 281 
to this hypothesis. Their sculpture presents suspicious 
points of resemblance to that obtaining in some meteorites. 
The basic constitution of meteorites is an opposed fact, but 
Dr. Suess replies that no valid reason can be adduced for 
denying to cosmic bodies the presence of acid silicates cor- 
responding to the most acid magmas of the earth’s crust. 
Professor F. Exner states that he has determined spectro- 
scopically the presence of nickel in Bohemian moldavite 
glass. If this determination is substantiated, it forms a 
strong support of the theory of cosmic origin. The giass of 
the Australites fuses with difficulty and without imtum- 
escence, unlike many obsidians. Mr. T. Stephens* in his 
most recent note on the subject, advocating a new terrestrial 
origin, says:—“ The ellipsoidal shape, which is not uncom- 
mon in Australian specimens of the buttons, is inconsistent 
with the theory of a long rotatory flight through the air, 
for any such volcanic ejectamenta must have cooled too 
quickly to allow of any change of form on reaching the 
ground.” This appears a valid objection to the derivation 
from distant volcanoes. It does not apply to the meteoritic 
hypothesis, which supposes the bombs to be re-fused frag- 
ments of a cosmic body which exploded or burst possibly 
within the limits of the earth’s atmosphere. It is, however, 
evident that the last word has not been said on this su} bject. 
SYENITE. 
Syenite is a near relation of granite. It is virtually a 
granite deprived of its quartz, or at all events of most of it, 
for there are few cases in which it is absolutely quartzless. 
The silica contents, generally 55 to 65 per cent., cause it to be 
regarded as a rock of the series intermediate between granites 
and gabbros, acid and basic. The molecular proportion of 
alkalies reaches about a unit in advance of the granites, 
averaging about 8 per cent. Normal syenite consists of an 
alkali felspar, usually orthoclase, with .a subordinate. amount 
of lime-soda felspar, usually oligoclase-andesine, accompanied 
by biotite, hornblende, and (or) augite. Like granite, the 
family is best sub-divided according to thecoloured minerals. 
Consequently we have hornblende-syenite, biotite-syenite, 
augite-syenite, none of these minerals absolutely excluding 
the other. 
So far in Tasmania, I have not met with a syenite in which 
biotite is the dominant magnesian ingredient. The other 
two divisions are represented. Hornblende-syenite, or 
* A further Note on Obsidian buttons : Proc. Roy. Soc. Tas., 
