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places. On the north side are the granitic rocks of the 

 plateau, on which the quartzite reposes. On the south this 

 quartzite — which is sometimes conglomeratic — is backed up, 

 apparently quite conformably, by massive dolomitic limestones, 

 micaceous clay slates, shales, and thinner bands of limestone. 

 Farther out (south) other quartzites, limestones, sandstones, 

 shales, etc., occur. The former are seen to be much fractured, 

 jointed, contorted, and displaced, and this is a feature of the 

 Cambrians in contradistinction to ail other strata. Eastward 

 from Mount Undoolya the dolomitic limestones spread them- 

 selves out more than elsewhere, and continue so to Love Creek 

 station. Earth movements and pressure have rendered it 

 somewhat difficult to determine the actual contact line between 

 the Cambrian and Ordovician ; the greater dynamic and 

 chemical effects upon the former, however, render a discrim- 

 ination possible. The same causes have obliterated all trace 

 of organic life except in most favourably-situated localities. 

 Diligent search through many years failed to discover fossils 

 in this formation, but in September, 1912, the author was 

 fortunate enough to discover fossils in the dolomitic limestone 

 which have since been determined by Mr. Walter Howchin, 

 of the Adelaide University, to belong to the genus Cryptozoon. 

 The spot where the discovery was first made is situated 

 about half a mile west of the old Acacia Well, on the north 

 side of the mail road from Alice Springs to Arltunga. 

 Acacia Well lies about ten miles south-east from Mount Ben- 

 stead and midway between that mount and Love Creek 

 station. It is also about ten miles west of Bitter Springs. 

 The fossiliferous strata form the northern boundary of one of 

 those long narrow valleys of erosion, so characteristic of the 

 South MacDonnell Ranges. The valley is about a mile wide. 

 On the south it is bounded by a steep-sided massive reddish- 

 coloured range composed of limestone, shale, sandstone, 

 quartzite, etc., rising 600 to 800 ft. above the valley. The 

 strike of all the rocks hereabouts is, roughly, east and west, 

 and the (estimated) dip varies between 35° and 75° to the 

 south. The valley here, and also for several miles both east 

 and west, is bounded on the north by a dolomitic limestone 

 range, 500 to 800 ft. high. The well is close to the range, and 

 the road runs under the range quite close to the fossiliferous 

 beds, which form the outer layers that run down and meet 

 the alluvium that covers the floor of the valley. Some of the 

 fossiliferous layers are only 2 and 3 inches thick, while others 

 are massive, being yards through. The aggregated thickness 

 is considerable — as seen where small creeks break across the 

 strata — and there is no lack of material, though good speci- 

 mens have to be searched for. The fossiliferous strata 



