Anniversary Address. 11 



the outward coating which distinguishes so many of the surface 

 pebbles found in the very heart of the interior of Australie? 

 traversed by Sturt, M'Kinlay, and Burke and Wills. "What 

 may have been the way in which these pebbles have been 

 polished, is not easy to be discovered. Iron sand, or, 

 better still, perhaps gem sand, in violent motion, may have been 

 the agent, since we know granite rocks in sandy deserts are 

 polished by sand-flows far from water. It has been suggested, 

 that the polish arises from the action of silicated water, as the 

 hollows in the pebbles are as smooth as the general surface. 

 But they are only in the condition of the greatest part of the 

 surface drift all over the interior of New Holland. Unless, 

 therefore, we assume, that a flood of silicated water has covered 

 the greater part of New Holland, we cannot so explain the 

 phenomenon.* If, on the other hand, the gems and the iron 

 belong to the basaltic rocks, and if these are younger than the 

 cement, such an explanation can only be accepted in connection 

 with a much more distant origin for the pebbles than any local 

 strata. The older drift, therefore, cannot have a local origin. 



It is certain, moreover, that if the other gems have been derived 

 from basaltic rocks, and not from the greenstone, of which there 

 is no evidence, the basalt was of an older period than that which 

 now covers the drift, and such older basalt is not traceable. All, 

 therefore, favours the belief that the term drift, implying a 

 driving of material from a distance, is a correct term to apply 

 to the Diamond-bearing deposits ; but a question of another 

 kind immediately suggests itself, — AVas the motive power of this 



* On comparing some epecimens of Cetacean remains and teeth of Carchar- 

 odon, brought more than forty years ago from the beach at Fehxstow, in the 

 County of Suffolk, (which fossils are certainly older than those in the crag 

 cliffs above, and appear not to have fallen but to have been drifted up from a 

 probably Miocene submarine bed. to the eastward.) I recognise the identical 

 kind and degree of polish on these Tertiaiy relics as distinguishes the Cudgegong 

 pebbles. This, at any rate, is an interesting fact, and may have some bearing 

 on geological inferences beyond the present use of it. In the superficial local 

 driit above the lerruginous sandstone beds about Sydney, are numirous 

 polished pebbles and iragments ot the rock v?bich exhibit an oxidised suiface, 

 but the polish in that case is, probably, due to very different agency to that of 

 a deposit upon the pebbles, which is tbe theory of those who regard the 

 Cudgegong pebbles as coated by an infiltration of silica. The Miocene 

 fossils on Fehxstow beach have, in the p/esence of iron, more relation to the 

 Sydney fragments than to the drilt pebbles of Cudgegong and the interior— 

 but there, lor the present, the comparison rests. 



