ANALYSES OF CHOCOLATE SHALE AND TUFACEOUS SANDSTONE. 157 
Chocolate Shale.—This is a fragment of chocolate shale 
and was obtained from Long Reef near Manly, where the 
chocolate shales outcrop on the sea shore. It is a dark 
reddish-brown ferruginous looking specimen of fine muddy 
shale. It displays a slight shaly cleavage but easily 
crumbles to pieces in all directions. Beyond this no 
definite structure is visible in the hand specimen. There 
are a few small greenish spots stained with copper. This 
specimen is very much weathered, and accordingly differs 
in appearance from the perfectly fresh chocolate shale, 
such as that obtained from the Balmain Coal Mine in the 
course of shaft sinking. It is probable that there is a 
corresponding difference in the composition, so that an 
analysis of the unweathered shale would, in all likelihood, 
differ materially from the present one. 
The unweathered shale is a clean rich chocolate coloured 
shale, composed of very fine impalpable material. It 
possesses a very indifferent shaly cleavage, and for the 
most part crumbles to pieces on exposure to the air. A 
transparent section of the fresh shale when seen under the 
microscope generally reveals a number of small concre- 
tionary blebs of siderite scattered through the fine, reddish- 
brown, homogeneous ground mass; these small concretions 
often exhibit a radial structure, and may be present in 
great numbers or be almost absent. Hence in rock that 
has not been weathered and oxidised, the proportion of 
carbon dioxide would probably be greater. 
