BY PROFESSOR STEPHENS. 337 



the thoracic plate of Mastodonsaurus (?) determined by myself.* 

 It is an extraordinary instance of survival, but is here especially 

 interesting as proving the estuarine character of at least this stage 

 of the Hawkesbury formation in the Sydney area ; a view which 

 I confess seemed to me so inconceivable, in the previous entire 

 absence of maiine remains, that I readily accepted this fossil, 

 without examination, as a freshwater mollusc. It is important to 

 remember with regard to these Hawkesbury Sandstones, that they 

 also, at least in the upper portion, offer sufficient evidence of 

 Glacial action, as has been particularly shewn by Mr. Wilkinson, 

 and by Mr. David in a paper on Glacial action in Australia 

 read before the Geological Society, Q.J.G.S., May, 1887, although 

 it does not seem to have met with a very cordial reception, "f 



I quote again from Mr. Wilkinson : " The surface of the 

 Hawkesbury Formation was denuded and worn into hollows before 

 the Wianamatta beds were deposited." (See also Clarke, Sedimen- 

 tary Formations, &c., p. 72), ''and the latter in their lithological 

 characters show that great physical changes must have taken place, 

 for they consist chiefly of argillaceous shales, which are in striking 

 contrast with the thick bedded arenaceous rocks underlying them. 

 The fine sediment which formed the Wianamatta shales evidently 

 settled down in the quiet waters of a lake." Thbmfeldia odon- 

 topteroides, Alethopteris Gurrani, Odontopteris Knicrophylla and 

 Phyllotheca Australis continue from the Hawkesbury, but Macro - 

 tceniopteris Wianainattce and Gleichenia sp., appear as new species. 

 The genus Palceoniscus is common to both, and both yield 



♦This genus, on account of the siphonal openings, has led to the removal 

 of the family from the Heteropoda to " a position near the Fissurellidaa 

 and Haliotidse, and between these groups and the Pleurotomariidae." 



tin the discussion of this paper Professor Boyd Dawkius is reported to 

 have said that " he had found Olossopteris to the west along with Lepido- 

 dendroid plants of Mount Victoria." I suppose we should read '^Glos^opteris 

 along with Lepidodendroid plants to the west of Mount Victoria." There is 

 plenty of Glossopteris, but if any Lepidodendroid fossil was found there it 

 must have been a lower carboniferous or upper devonian form, possibly 

 from Mount Lambie, or perhaps as a transported and foreign fossil from 

 the upper marine (glacial) beds. 

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