245 



quartzites : the Magill and Fourth Creek exposure, to the 

 Fourth Creek and Black Hill quartzites, and, in each case, 

 the limestone, thout^h stratigraphically superior to the 

 quartzites, is thrown down to the west. At Anstey's Hill, 

 however, where the quartzites are tipped to the east, the blue 

 limestones are also thrown to the east. This stratigraphical 

 association of the two sets of beds throughout the district 

 (notwithstanding the disturbed condition of the field), estab- 

 lishes the order of succession and materially assists in fixing 

 the main fault-planes. 



VIII. — The Phyllites and Lower Limestone 

 CRiver Torrens Limestone). 



A pJiyllite is an argillaceous rock of a micro-crystaliiue 

 structure. It differs from clay-slate mainly in its more schis- 

 tose character. It is generally laminated ana wavy, and the 

 development of sericitic mica gives it a lustrous appearance. 



There is no sharp line of distinction between the Glen 

 Osmond slates, which are sometimes phyllitic (especially in 

 their lower members), and the phyllites proper, winch occupy 

 a geological horizon beneath the thick quartzite described 

 above. The development of the phyllitic structure appears to 

 have been mainly determined by the measure of folding lo- 

 cally developed ; the greater the crush the more distinctly are 

 the phyllitic features manifest in the beds. 



These beds outcrop on the north side of the Black Hill, 

 are well seen in gullies facing the west ; and also in the Tor- 

 rens River, above the weir, where they have yielded a 

 small amount of copper. The phyllites occur on the east 

 side of Mount Lofty (rising from beneath the quartzite). and 

 from their decomposition the productive garden soil of Picca- 

 dilly, situated in the valley, has been mainly derived. The 

 Mount Lofty Park Mine (Section 840, Hundred of Onkapar- 

 inga) is in these beds. The ore is mainly sphalerite (zinc 

 sulphide), with a little galena and iron pyrites. The phyl- 

 lites at this place dip south-east at 30°, and the lode, which 

 does not exceed 4 inches in width, has well-defined walls, and 

 hades to the north at 80°. Not much quartz is present in 

 these slates, a feature in which they show a strong contrast to 

 the Pre-Cambrian slates of the district. The dip of the beds 

 increases to the eastward, where they become vertical, or dip 

 east at a very high angle. 



The phyllites are often strongly chloritic, giving the 

 stone a green colour, and along lines of great disturbance, ac- 

 companied by quartz veins, the mineral chlorite is often found 

 in considerable quantities. The contemporaneity of the 



