Basal Grits, etc. 

 The basal beds of the Cambrian here, as for the most part 

 elsewhere, consist of coarse arkose grits. The fragments of 

 felspar are often large, angular, sub-angular, or rounded ; as 

 also are the quartz grains. The beds are coarsest near the 

 bottom of the series, and pass up into finer material as 

 quartzites of the normal type. The junction of these bottom 

 grits with the Pre-Cambrian can be well seen along the western 

 limits of the Pre-Cambrian, on both sides of the river. In 

 Sec. 5598 (Onkaparinga) the line of junction follows, mainly, 

 a small lateral creek, the Pre-Cambrian gneissic beds being 

 exposed on the northern banks of the creek and the basal grits 

 on the southern side. The line of demarcation is here, how- 

 ever, a little irregular, as the northern side forms a dip-slope 

 and the removal by denudation of the overlying grits has been 

 partly determined by the lie of the ground. The basal beds 

 can be traced along the flanks of the ridge on the south side 

 of the Torrens, through Sec. 335 (Onkaparinga) down to and 

 across the river at the ''galvanized-iron hut," not far from 

 Kangaroo Creek. 



Lower Torrens-Limestone. 



There are two limestones near the base of the Cambrian 

 series. These can be distinguished from each other by their 

 lithological features, as well as their stratigraphical position 

 in the series. 



The lower limestone is a granular, crystalline, white and 

 buff-coloured rock, generally more or less schistose with 

 sericitic faces and small flakes of talc. The bed is over 100 ft. 

 in thickness and is moderately uniform in composition, but is 

 broken by numerous bedding-planes and joints. 



This limestone, like the basal grits, skirts the Pre-Cam- 

 brian massif in a roughly semi-circular contour. Its most 

 northerly position in this locality, known to the writer, is at 

 Highercombe House (Sec. 5520, Yatala), where it was proved 

 in sinking a well in the kitchen of the house. From this 

 point it can be traced southwards, through Highercombe 

 orchards and along the western banks bordering Goodwin 

 Creek, down to the River Torrens, where it is seen in the angle 

 of the river in Sec. 334 (Onkaparinga). This is, perhaps, the 

 most important outcrop of this limestone in the district, and 

 is known as ''Marble Bar." The limestone makes a wide 

 spread in the bed of the river, taking the form of three parallel 

 ridges of rock, covering an area of about 100 yards wide, (a) 

 The central ridge is at the acute bend of the river where Good- 

 win Creek joins the main stream. The strike is north-west 

 b2 



