156 S. G. WALTON. 
The methods followed and quantities of reagents used 
were those detailed by Hillebrandt and Washington. Hach 
estimation was made in duplicate, and only the purest of 
reagents were used, which were all tested, and where 
necessary, aS in the case of calcium carbonate, specially 
purified. I regret being unable, through want of time, to 
estimate the amount of vanadium present. Iam indebted 
to Mr. R. S. Bonney, B.A., of the Geological Laboratory, 
Sydney University, for the following descriptions of the 
specimens : 
Tufaceous Sandstone.—This rock belongs to the Narra- 
been beds, and is a green tufaceous sandstone containing 
small rounded pebbles of green and redchert. As seen in 
this section the fragments composing the rock are rounded 
and subangular in outline. 
The chief constituents are:—1. Subangular fragments of 
quartz and felspar. 2. Fragments of decomposed igneous 
rocks, some grains of which contain numerous small felspar 
laths. There is one small grain of micrographic granite 
in the slide that was prepared. 3. A green chlorite 
decomposition product occurring plentifully throughout the 
slide. It appears partly in the form of grains, mostly 
rounded; partly asa very narrow border due to secondary 
decomposition, (not marginal decomposition) round all the 
other fragments, quartz included; and occasionally as an 
interstitial infilling. This mineral is very common in the 
Narrabeen rocks, but never occurs in the Hawkesbury 
Sandstones. 4. Small round grains and pebbles of green 
and red chert. Bands of coloured chert pebbles are of 
very common occurrence in the lower half of the Narra- 
been rocks. The thin section reveals a great variety of 
constituents, but most of them are included in the above 
four classes. Siderite, which is usually plentiful in the 
Narrabeen rocks, is not present in this slide. 
Bite gens - 
