The Upper TopvREns-Limestone. 



The Upper Torrens-limestone is, as a rule, bluish in 

 colour and somewhat slatey; but in places it takes on a more- 

 calcareous form and becomes subcrystalline. It is an impure 

 limestone, with much earthy and siliceous matter included, 

 and, under weathering, exhibits wavy mineral lines in relief. 

 It also carries black cherty-quartz, both as nodules in the 

 limestone and also as cherty bands. The latter are sometimes 

 found as surface stones when the calcareous contents have been 

 largely removed by solution. It is often found along depressed 

 surfaces, the limestone having suffered greater waste than the 

 associated siliceous beds. When this limestone forms scarp- 

 faces the stone has a characteristic black surface, arising from 

 the growth of a dark-coloured lichen on the face of the stone. 

 The more calcareous, portions are interbedded with a dark- 

 coloured, carbonaceous-looking blue slate, which is often a 

 guide to the discovery of the blue limestone in the adjacent 

 rocks. At Teatree Gully ^^^ it is quarried, burned, and manu- 

 factured into a lime-cement. 



In the much-faulted district of the River Torrens, now 

 under description, the blue limestone is greatly interrupted 

 and follows many diverse lines of strike. The general trend 

 is that of an outer circle to the Lower Torrens-limestone in 

 investing the Pre-Cambrian massif, and in its err'atic course 

 sometimes approaches very close to the lower limestone, but in 

 other places becomes far removed from it. The steep, hilly 

 country has also had something to do with determining the 

 erratic nature of the strike. An examination of the geological 

 map (facing page 1) will make this clear. 



Monfdcitfe. — An important outcrop of these beds is found 

 at the top of the "Corkscrew," on the ridge at the back of 

 Montacute Church, where it has been quarried for road metal 

 (dip south-east at 50°). It can be followed for some distance- 

 on the western side of the hill, parallel to the road that 

 descends from the hill-top towards Adelaide. Another out- 

 crop, about on the same level, is seen just inside of the fence^ 



(1) In my Greology of the Mount Lofty Ranges,, pt. ii.. Trans. 

 Roy. Soc., S.A., vol. xxx. (1906), p. 239, I erroneously referred the- 

 blue limestone of Anstey Hill and Teatree Gnlly to the "bhie 

 metal" limestone, which it much resembles; but the latter occurs 

 higher in the series. The "bine metal"' limestone outcrops alontr the 

 western slopes of the foothills, further to the south. The occur- 

 rence of a similar limestone at Teatree Gully was referred, in the^ 

 first instance, to the same geoloo;ical horizon, a mistake that might 

 easily follow from the disturbed and complex arrangement of the- 

 rocks that occur at that point. 



