BY T. W. EDGEWORTII DAVID AND WALTER HOWCHIN. 581 



vertical dips are not uncommon. We think it probable on this 

 account, as well as on account of its lithological character, 

 tlaat this series is also Pre-Cambrian, perhaps on about the same 

 hox'izon as the siliceous limestones exposed in the vineyards 

 at Burnside, near Adelaide. Moreover, no macroscopic fossils 

 have been observed by us in these limestones, in spite of their 

 having suffered extremely little through metamorphism, whereas 

 the local Lower Cambrian limestones are abundantly fossili- 

 ferous, and only slightly inclined, without distinct folding. At 

 the same time, the fact must be mentioned that the Crystal Brook 

 radiolarian locality lies directly in the trend of the Cambrian 

 rocks from Yorke's Peninsula N. by E. towards the Blinman Mine 

 to the N.N.E of Port Augusta. On the whole, however, we 

 think that the evidence is in favour of the radiolarian rock at 

 Crystal Brook being Pre-Caralirian. 



5. Summary and Provisional Deductions, &c. 



(i.) At Brighton and Crystal Brook in South Australia (their 

 respective positions are shown on PI. xl. fig. 3), rocks are 

 developed which contain what appear to be casts of radiolaria. 

 At the latter locality there can be little doubt, in our opinion, as 

 to the identity of the casts with those of radiolaria. 



(ii.) That the age of these rocks is Pre-Cambrian is i-endered 

 highly probable by the following considerations : — 



(a). The local Lower Cambrian rocks are "gently inclined at 

 angles of from 8° to L5°, and they are not folded, whereas the 

 radiolarian rocks dip at 45° to 80°, are considerably folded, and 

 seem to underlie unconformably the Lower Cambrian formation. 



(b) The Lower Cambrian rocks of South Australia are pure 

 and massive pteropod ' limestones, whereas no such beds of pure 

 thick limestones are to be noticed in the radiolarian group. 



(c) The Lower Cambrian limestones of South Australia contain 

 a rich and abundant macroscoj^ic marine fauna, whereas no 

 macroscopic fossils have ever ]:)een found amongst the Brighton 

 and Crystal Brook radiolarian rocks, although the rocks at both 



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