236 



directed from the east tawards the west, and has resulted in 

 the stronger quartzites making overfolds, ana crusiiing or 

 overriding the slates. The slate-bed which overlies the quartz- 

 ite of the round hill at Mitcham, for example, has had a 

 sharp throw-down to the west, as seen in an old quarry in a 

 by-road, on the south side of the township. The beds are 

 vertical, wavy in the grain, and exhibit several nearly hori- 

 zontal thrust-planes in a movement from east to west, by 

 which the vertical beds have been broken and slid along planes 

 at right angles to the bedding. Fine examples of thrust can 

 also be seen in cuttings on the new road between Magill and 

 Norton Summit. 



The thickest of these slate-beds occurs immediately below 

 the Glen Osmond quartzite. The junction of these beds (which 

 also exhibits a remarkable illustration of thrusts) can be dis- 

 tinctly seen in the large quarry which has supplied much of 

 the building stones of Adelaide and district. The slates rise 

 from beneath the quartzite, at a low angle of dip, and extend 

 in the direction of Mount Lofty, as far as the Eagie-on-the 

 Hill ; down the Waterfall G ully, and in a northerly direction, 

 they form the grassy foot-hills which run parallel with the 

 ranges. In its upper portions it has the features of an earthy 

 slate, with cleavage imperfectly developed, but near the base 

 it is often a typical phyllite. This bed forms the dominant 

 outcrop on the western flanks of the Mount Lofty Ranges, 

 and is probably not less than 2,000 ft. thick. 



Towards the bottom of this thick slate several beds of 

 quartzite are intercalated. These can be seen on the Glen 

 Osmond road, between the Eag-le-on-the-Hill and Crafers, and 

 also in the Fourth Creek (Morialta), where one of the beds 

 makes a scarped cliff on the south side of the gorge, where 

 the softer beds are strongly sericitic. 



At the Fourth Creek and Stony fell, as well as at other 

 localities, the "thick quartzite" (which underlies the ''thick 

 slates," and will be described presently), has been sharply 

 curved towards the west, sometimes overfolding, and has 

 thereby thrown the overlying thick slates down to the west, 

 forming the clay foot-hills referred to above. It is from this 

 movement that the Glen Osmond slate-beds have such an ex- 

 tended area in a northerly direction. The stratigraphical 

 sequence of these beds is materially simplified by the j^res- 

 ence in them of a calcareous belt, which is moderately con- 

 stant in its features, and forms a definite horizon in the series. 

 It includes an impure limestone, locally known as "blue 

 metal," which has been extensively used for road-making. 

 The stratigraphical importance of these beds requires sepa- 

 rate reference. 



