382 



Sedimentary Series at the Bolla-Bollana Gorge. 



A great quartzite formation is cut across by the Bolla-Bollana Creek at 

 the spot known as the Gorge. There the bed is roughly 500 feet thick and 

 strikes N. 30° E. In places it shows evidence of folding, but for the most part 

 dips steeply to the south ^^^ (about 60°). Beds of grit and pebbles are included, 

 and in them the pebbles are chiefly quartz and quartzite, but there are also many 

 dark coloured ones of basaltic appearance and light coloured felsitic types, some 

 of which were noted to be epidotised. 



The finer-grained section of this quartzite formation is ripple marked and 

 shows fine current bedding features. There is present a small quota of oxide 

 of iron in fine grains arranged in laminae, of which 60 major laminae were 

 counted in 6 feet of the rock. Some of this original black iron sand has been 

 converted to hematite and impart a slight reddish tinge to some areas of the 

 rock. 



Above this quartzite follow several hundred feet thick of beds ranging from 

 a very fine-grained sandstone below, then shaley beds and finely calcareous slates. 

 The relation of these beds to the quartzite below was not determined, as no clear 

 contact came under notice, but it was assumed that they follow regularly above 

 the quartzite. 



Now follows a definite unconformity. A coarse conglomerate is seen in the 

 creek dipping to the S.S.E. at a much lower angle than the underlying beds just 

 described. Where weathered the sandy matrix has crumbled to a large extent, 

 and the boulders show up well. These latter are rounded and subangular. No 

 glacial striae were observed, but the time available gave no opportunity for 

 making a proper search. Though not at all a typical tillite in character, this 

 boulder rock, nevertheless, has certain characters which suggest a glacial or 

 fluvio-glacial origin. This conglomerate formation constitutes what appears to 

 be the base of an extensive series outcropping to the S.S.E. in low undulating 

 hills. Unfortunately there was no opportunity for a reconnaissance in that 

 direction. The general lithological features of the beds suggested, at the time, 

 the Adelaide Series (Proterozoic) ^^^ as exposed widely in the North Flinders 

 Range further to the west. This view is strengthened by the fact that, what 

 appears to be a glacial tillite horizon higher up in this same series was reported 

 by Mr. W. B. Greenwood ^^^^ to cross the Arkaroola Creek a few miles lower 

 down at a spot two miles east of the Kingsmill Mine. 



Reverting to the detail of the conglomerate formation, boulders were noted 

 near its base identical in character with the underlying shaley sandstone. Above, 

 the great bulk of the boulders, especially the larger ones, are identical with the 

 great quartzite in the gorge, for example, exhibiting the very striking regular 

 fluting due to a characteristic arrangement of the iron sands under the influence 

 of a flowing water. One of the boulders measured 3 feet 6 inches in diameter. 

 Very few are more than 2 feet and most are but a few inches in diameter. Other 

 types of rocks noted were a red-tinted quartzite, a dense gritty quartzite, and 

 several large blocks of grit just like that at the base of the shales below. Many 

 of the boulders were so far weathered as to be unrecognizable, though several 

 suggested decayed felsites. Neither granitic nor basaltic rocks were recognised. 

 Though the traverse probably did not reach the limits of the boulder bed, a 

 thickness of fully 500 feet was recorded. 



(8) The field note-book says dipping "north," but this appears to be contradicted by later 

 entries, and is therefore taken to be a clerical error. 



(9) Sir Edgeworth David, Trans. Roy. Soc. S. Austr., xlvi., 1922, p. 6. 



(10) Private communication. 



