312 



down, almost vertically, probably 4,000 feet, and has become 

 shattered, brecciated, and mylonized during the movement. 

 It might be comparable to a ''thrust" that was nearly vertical 

 in movement. (22) 



UPPER TORRENS-LIMESTONE ([ ?] Enterolithic). 



The Upper Torrens-Limestone is a dark-coloured, earthy 

 and siliceous limestone that occurs in the Lower Cambrian 

 rocks towards the base of that series. The bed carries much 

 black chert (23) which occurs in the form of nodules, lenticlea, 

 and layers. In some localities the chert consists of two very 

 distinct materials (pi. xvi.), the matrix consisting of a light- 

 coloured siliceous base, and in this groundmass there are 

 thickly studded angular and rounded fragments of black 

 chert. The round, pebble-like inclusions vary in size from 

 that of oolitic grains up to half-an-inch in diameter and are 

 not concentric in structure. The angular fragments are flat 

 with vertical sides, and are often about an inch to two inches 

 in length and about a quarter of an inch in thickness. There 

 is no very distinct stratigraphical order in the arrangement 

 of the respective inclusions, for while there is a rough kind 

 of parallelism in the way in which they • occur in the rock, 

 they may lie at any angle. 



One of the localities in which they occur very abundantly 

 is near Frewville, on the Port Germein road, three miles west 

 of Booleroo Centre. The geological features of the district 

 are much obscured by arable land. The Cambrian tillite 

 crosses the Port Germein road about a quarter of a mile to 

 the eastward of the Gorge Hotel, with quartzite below and 

 the Tapley Hill banded slates on top, dipping east. Very 

 little rock can be seen till the Port Germein road meets the 

 main north road, a little south of Murray Town, where the 

 banded slates are again seen in a quarry near the road with 

 a dip west. On the hill-top above Frewville there are 

 exposures of slates and sandstones with a dip west at 40°, 

 and, nearby, both in heaps by the road and scattered over the 

 paddock (Sec. 54, Hd. of Booleroo), there are large numbers 

 of cherty fragments with brecciated inclusions. The specimens 

 seen were all surface stones, the outcrop probably forming the 

 subsoil of the ploughed ground. Although not seen in situ 

 here, there is little doubt that the chert was derived from the 

 Upper Torrens-Limestone beds. Good examples also occur 



(22) For further particulars see Howchin, ''The Geology of 

 Mount Remarkable," Trans. Roy. Soc. S. Austr., vol. xl. (1916), 

 p. 545. 



(23) Howchin's "Geology of South Australia," p. 356. 



