263 
always very apparent between the two beds, as the upper part 
of the blue limestone is often mottled with patches of a pink- 
ish colour. In parts, it exhibits a similar oolitic structure, 
as shown by the pink limestone. It contains 40 per cent. or 
more of silica. It is fairly uniform in composition, and is 
applied to the same economie uses as the overlying bed, being 
worked up in the manufacture of cement, and is locally 
known as the “blue metal limestone," from its application to 
road-mending. Tt frequently carries crystals of pyrites and 
amethystic-coloured cubes of fluorite. At Brighton, large 
globular and mammillary crusts of barite have occurred on 
the surface of the blue limestone, the mineral having a finely 
fibrous structure and silky lustre. 
(d) The lowest member of the group comprises a series of 
dark-coloured, very siliceous limestones, of variable composi- 
tion, but much more siliceous than the over-lying bed (с). 
Indeed, the beds vary from distinctly characteristic siliceous 
limestones to earthy, calcareous shales. This division, as 
a whole, is distinguished by the possession of a faintly lami- 
nated structure, which, on  weathering, becomes more 
strongly marked. At some horizons the siliceous limestones 
exhibit in vertical (weathered) sections a peculiar vermicu- 
late structure, which, at first sight, is very suggestive of fos- 
sil remains. On splitting the stone parallel to the bedding 
planes it is seen that this effect is produced by the occur- 
rence of thin, wavy films of mineral matter in irregular 
patches. "This striking feature is very characteristic and per- 
sistent, and forms an excellent means of fixing the geological 
ltorizon when these beds are seen in outcrop. 
The above caleareous division, which for convenience I 
have grouped under the heading of the Brighton limestone 
series, takes rank as one of the best-marked horizons in South 
Australian geology. Тһе belt can be easily traced in out- 
crop from Brighton, southwards, to Reynella and Hallett's 
Cove. At Hackham it has been extensively quarried. 1t 
crosses the Onkaparinga about a mile above Noarlunga, and 
can be traced further southwards until it disappears under 
newer deposits, shortly before reaching Aldinga. Its north- 
erly extension is, in the first instance, obscured by the 
alluvial of the Adelaide and Gawler Plains, but it re-appears 
at the Burra, Mount Remarkable, Orroroo, Walloway, etc. 
The diversity of its economie products may be seen in that it 
has been worked for road metal at Reynella and other 
places, cement at Brighton, copper at the Burra, phosphates 
at (?) Fairview, and flux at Orroroo. The relative thinness of 
the beds and their solubility have led to their denudation 
over vast areas where thev formerly existed. 
