FROM THE TERTIARY DEPOSITS OF TASMANIA. 345 



The sclerenchyma, as a whole, may be said to consist of spicules 

 radiating from centres in more or less linear series ; and each spicule 

 is joined laterally and before and behind to its fellows. The whole 

 coral is infested with the tube-like penetrations and ramifications of 

 a parasitic unicellular Alga ; and this has been described in a former 

 communication (see Quart. Journ. Geol. Soc. vol. xxxii. p. 205). 



Remarks on the Species. 



The Heliastrsean just described was evidently a rapid grower, and 

 a true reef-building form, having its bathymetrical distribution 

 restricted to 20 fathoms ; and the Thamnastraean (so solid, yet so 

 abundantly supplied with endothecal structures) appears to have 

 had a corresponding habitat. They required the external conditions 

 peculiar to coral-reefs. 



In considering how these physical conditions could be found on 

 the area from which their absence is now so conspicuous, the general 

 physical geography of the Australian seas during the Cainozoic 

 periods must be considered. This was attempted to be ex- 

 plained in 1870 (Quart. Journ. Geol. Soc. vol. xxvi. p. 284), by the 

 author of this communication ; and the relation of the past 

 and existing coral-faunas of Southern Australia, and the former 

 distribution of land and sea, were noticed in the concluding parts of 

 his essay on the fossil corals of the Australian Tertiary deposits. 

 As there is no reason for altering the opinions therein expressed, 

 reference must be made to that communication ; and the bearings of 

 the suggestions therein contained will be found to be explanatory 

 of the existence of reefs in Tasmania. The open sea of the vast area 

 to the west of Cape Howe, running up into the tropics, would place 

 the old hills of Tasmania' and those of Eastern Australia in the midst 

 of an ocean, even if the Australian land were prolonged away to the 

 north-east, as it probably was in those days. But even admitting 

 that probable insular distribution of land in the South Pacific during 

 the Miocene epoch which has been so frequently suggested by 

 zoologists, botanists, and geologists, the fact of the sea-temperature 

 being sufficient for the development of reefs in Tasmania is insuffi- 

 ciently explained. 



There is a faint relic of the old reef-fauna still lingering on the 

 Tasmanian shores in the form of Echinopora rosularia, Linn. It 

 forms thin incrusting layers, and not masses of limestone ; but it is 

 clearly a relic of that reef-building coral-fauna which has long since 

 died off from the area. Even the hardiest of the Pacific corals, the 

 stronger forms of Porites, are absent. In fact, the only surface- 

 water coral lingers on in a temperature in which Porites could 

 neither exist nor propagate. 



Evidently the reefs around Tasmania, now long extinct, existed 

 amidst all the physical conditions peculiar to coral-growth on a 

 large scale. Pure sea- water in rapid movement and having a 

 temperature of not less than 74° Fahrenheit, was as necessary to 

 them as it is to those far away to the north and north-east at 

 the present day. 



