BY T. W. EDGEWORTII DAVID AND WALTER HOAVCHIN. 577 



above which no hmestones, serviceable for cement or lime, are 

 met with. 



2. Puik-coloured Limestone. — This bed is sharply defined from 

 the preceding by a bedding plane. It is about 15 feet in thick- 

 ness, of a pale pinkish colour, and carries about 86 per cent, of 

 carbonate of lime — the purest limestone in the group. The 

 weathered faces of the vertical joints exhibit lines of false bedding. 



3. Blue siliceous Limestone. — This immediately underlies the 

 pink-coloured limestone, and in the upper portions of the bed is 

 frequently mottled by various sized pinkish patches. It contains 

 forty per cent, or more of silica. The pink-coloured patches con- 

 tain a lower proportion of silica and correspondingly higher pi-o- 

 portion of carbonate of lime, than the distinctly blue limestone. 



4. .Very siliceous dark-coloured Limestone of variable composi- 

 tion, but carrying more silica than No. 3. This bed, as well as 

 the one immediately above it, is strongly laminated. Whenever 

 this feature is present it is said to be an indication of a high 

 proportion of silica in the stone. This limestone is the lowest 

 horizon worked for cement, but the stone used by the companj- is 

 chiefly won from beds ISTos. 2 and 3. Immediately above this bed 

 is a calcareo-siliceous shale of very close texture. 



The beds have a strike about N. 12° E. The dip varies from 

 about 50° to 80° in a direction about W. 12° N. These Brighton 

 rocks may be considered the foothills of the Mt, Lofty Range, 

 towards and under which they appear to dip. Whatever, there- 

 fore, be the age of the Mt. Loft}^ Range, the Brighton rocks will 

 prove to be of at least as high a geological antiquit}^ 



The Mt. Lofty and associated ranges form the backbone of 

 the southern portions of South Australia, from Lake Eyre to 

 Kangaroo Island. In the neighbourhood of Adelaide, the western 

 flanks of the I'anges show alternations of clay-shales (often 

 micaceous or chloritic), quartzites, and siliceous limestones, with 

 an average dip of about 45°, and are considerably folded. At 

 Hallett's Cove, about five miles south from Brighton, several 

 sharp anticlinal folds occur near the coast and in the gorge of 



