13; 



showing mural scarjis that end in a bold, steep face to Sixth 

 Creek, in Mr. T. T. Trebilcock's garden, referred to above. 

 The blue limestone lies on the eastern side of this quartzite, 

 and can be traced from the top of the ridge, on Mr. Batchelor's 

 property — first, only by occasional surface stones, but it 

 gathers strength as it descends towards the bottom of the hill 

 (Sec. 5523), where it becomes a distinct and broad outcrop. 

 At high-level the strike of the limestone is 10'' east of north, 

 but as it descends towards the valley it swings round to north- 

 east, with a south-westerly dip at a high angle. The lime- 

 stone reaches the Sixth Creek near Mr. Trebilcock's house, and 

 is cut (like the same limestone a little higher up the stream) 

 by the north and south fault of the Montacute Mine. In this 

 way the blue limestone makes an almost complete circle of the 

 lower portions of Sixth Creek, following the left bank from 

 Mr. Trebilcock's garden as far as Mr. Smith's water-wheel, and 

 then returning by the right bank of the stream to nearly the 

 same spot in Mr. Trebilcock's garden, from which it started. 



GENERAL CONSIDERATIONS. 



The two main geological systems developed in the district 

 exhibit marked differences in physiographical form. The 

 Pre-Cambrian massif stands out in bold relief. Viewed from 

 the hills on the southern side — as, for example, from the top 

 of the ''Corkscrew," or from the ridges that enclose Pinkerton 

 Gully — it has the appearance of a tableland, edged with dark- 

 coloured, frowning rocks and thick scrub, rising to a height 

 of about 1,000 ft. above the level of the River Torrens, which 

 has dissected a southern fragment from the main mass. The 

 surrounding Cambrian beds are distinguishable from the Pre- 

 Cambrian complex by a sharply-defined passage into open 

 grass lands, gardens, and cereal cultivation. It is probable 

 that this great Pre-Cambrian inlier formed a monadnock when 

 the old peneplain passed below base-level at the beginning of 

 the Cambrian period. The lowest members of the Cambrian 

 series encircle the older land-form, and have been built up 

 by its waste. Near the points of junction between the two 

 systems the Cambrian beds dip away from the Pre-Cambrian 

 inlier in a curvilineal fashion, but at some distance away from 

 the base, the phyllites, as seen on the new road along the 

 Torrens gorge, have an easterly dip. Thus, just beyond the 

 limestone that outcrops at the sharp angle in the road below 

 the confluence of the Sixth Creek, the phyllites dip south-east, 

 at 35 '^ ; a little further west the dip becomes lO'^ north of east, 

 at 24°, and at the sharp north-east bend, in Sec. 553B, the dip 

 is 20° north of east, at 24°. 



