Tertiary Deposits of the Aire and Cape Ottvay. 53 



Professor Martin Duncan in speaking of our tertiary rocks says : 

 " Pure limestone, except in the upper part of the series is rare ; 

 it contains there an abundance of polyzoa, and is a deep-sea 

 deposit " (7, p. 286). In considering that part of this statement 

 with which we are at present dealing, it must be borne in mind 

 that ideas as to what constitutes a deep-sea deposit have greatly 

 changed since Duncan wrote this, nearly thirty years ago. In 

 the same volume of the Quarterly Journal his remarks show 

 (pp. 54 and 70) that he applies the term deep-sea deposit to 

 anything over ten fathoms, while for the great depths, then being 

 for the first time explored, he would employ the term abyssal. 



The organisms, of which the remains constitute the bulk of 

 the rock, probably lived in places where, though the water might 

 be many fathoms deep, yet strong currents prevailed, just as at 

 present the strongly calcareous polyzoa exist in the greatest 

 profusion with us at such places as Port Phillip Heads and the 

 entrance to Western Port, where the tide-current runs most 

 strongly and deposition of fine sediment cannot take place. 

 Limestones of a similar nature are now forming apparently in 

 the shallow waters in the neighbourhood of coral atolls as 

 described by Dana (19, p. 121), and more especially by sub- 

 sequent writers on the Lagoon of Funafuti. Professor T. W. 

 Edgeworth David has told us orally that the floor of the lagoon 

 is in many places covered with a thick deposit of foraminifera 

 which are even now in parts being cemented into a solid rock. 

 There is nothing then in the nature of the organisms, the remains 

 of which build up our polyzoal limestone, and the foraminiferal 

 limestone into which it in many places passes, which demands 

 deep water for their growth, while the physical nature of the 

 deposit, composed as it is of worn and broken fragments of 

 considerable size, is clearly an indication of its formation in very 

 shallow water or in places where strong currents run. 



One of the most interesting points about the eocenes of the 

 Aire, is the existence close together of two clearly distinct 

 faunas. The fauna at the Otway section has been already 

 dealt with by Messrs. Tate and Dennant, and its strong like- 

 ness to that of Aldinga has been noted by them (12, p. 113), 

 and the Castle Cove section belongs to tlie same horizon. In 

 contrast to the fauna of these beds is that displayed at Fishing 



