406 T. W. E. DAVID, W. F. SMEETH, AND J. A. WATT. 
in places show a fibrous structure. The green mineral appears to 
be au altered diallage. The evidence upon which this statement 
is based, has been derived from one of the sections, which shows 
the transition from a diallage to that of the green mineral under 
consideration. ’ 
Diallage. 
This mineral occurs in grains of irregular outline having a well 
marked parallel structure due to prismatic intergrowth, which in 
the coarseness of its structure resembles that of bronzite rather 
than that of typical diallage. The colour by transmitted light is 
a pale yellowish-green. The granules show cleavage cracks and 
microscopic inclusions, and a well-marked parting parallel to the 
orthopinacoid. Cleavage flakes taken parallel to this parting have 
straight exstinction, and exhibit the excentric emergence of an 
optic axis in convergent polarised light, a feature specially charac- 
teristic of diallage, and this admits of the determination of the 
optical sign of the mineral as positive. The double refraction is 
high, as indicated by the polarization colours, and the index of 
refraction is also high. The majority of the sections give oblique 
exstinction up to angles of 39°. 
NoTE ON THE OCCURRENCE OF A CALCAREOUS SANDSTONE 
ALLIED TO FONTAINEBLEAU SANDSTONE art 
ROCK LILY, near NARRABEEN. 
By Professor DavID, B.A., F.G.S. 
[Read before the Royal Society of N. S. Wales, August 2, 1893. ] 
CaLcaREous Sandstone has previously been recorded as occurring 
in the Tomago Series of East Maitland, the calcite being erystal- 
lised out in the mass of the sandstone, and also in rocks of the 
