88 Scientific Proceedings, Royal Dublin Society. 
and dust-like globulites; magnetite occurs in addition, sparingly 
dispersed in minute grains and octahedra. The pyroxene needles 
are incomplete hollow prisms, filled with glass; their edges 
are rarely continuous straight lines, but jagged with projec- 
tions which frequently develope on each side into secondary 
prisms, proceeding from the shaft, like the barbs of a feather, and 
these by continued growth tend to pass into an extended plate. 
The angle of extinction measured against the length of the 
primary prisms varies from 27° to 43°. The angle of the prism, 
owing to the minuteness and incompleteness of the crystals, is 
difficult to measure, but such observations as I could make sug- 
gested that of augite rather than hornblende. The colour is 
faint green, and there is no dichroism. The glass immediately 
Fie. 1.—Pyroxene and stellate crystallites in a glassy base. 
surrounding the pyroxene is usually clear and structureless, but 
at a very little distance away it becomes dark with granules, 
which under a high magnification are resolved into clusters of 
stellate crystaliites, wonderfully similar to the minute asters of a 
sponge such as Astropeplus or Thenea. The rays of these asters 
vary in number from two to ten or more, and are generally 
without action on polarized light; when, as in some instances 
is the case, they are birefringent, extinction is parallel. Some- 
times within a cluster of asters is seen a clear central space, and 
lying in this a comparatively large aster, with secondary raylets ; 
