BY H. J. JENSEN, D.SC. 76 



Wo opposite directions. As the lakes diminished in size 

 and the damp zone around them grew smaller, great herds 

 of animals A\ould draw together around their waters and 

 die of thirst when finally a drought dried up their drinking 

 supplies. In many parts of our interior great masses of 

 bones of extinct animals are found, and where such is the 

 case the neighbouring rock is likely to be a phosphatic 

 limestone, as we remember that limestone in particular 

 has a preservative action on bones. 



While some of the animals of the interior migrated 

 inwards towards the drying up lakes, other troupes migrated 

 outwards towards the Gulf of Carpentaria and the Great Aus- 

 tralian Bight. In both of these areas a considerable eleva- 

 tion has taken place in Pleistocene times, and Tertiary 

 deposits, essentially limestone rich in foraminifera, have been 

 raised high and dry, just as the Pleistocene of Florida has 

 been elevated. These troupes of animals always hugging 

 the moist coastal regions would in droughty years die in 

 great numbers, and their remains, when falling upon fora- 

 miniferal limestone or in cracks and crevices of such a forma- 

 tion, would give rise to phosphatic limestone or secondary 

 phosphorite. It is therefore possible that in the Tertiary 

 limestones, both of the Australian Bight and of the Gulf of 

 Capentaria, jDOckets of rich phosphatic rock, similar to that 

 of Florida, might be met with. 



(C) Bone Beds in Limestone Caves. — Several years 

 ago when rambling through some of the Chillagoe Caves of 

 Northern Queensland, I came upon some caves which 

 contained on the floor a bone bed at least several feet in 

 thickness. This occurrence is probably not an isolated one, 

 but common in our Northern limestone country. In such 

 bone caves phosphate rock of commercial value is possibly 

 to be found. 



{D) Guano. — In our limetsone formations, and especially 

 near the coast of Tropical Australia, where luxuriant shrubs 

 provide abundant feed for all varieties of animals, large 

 caves containing great thicknesses of bat guano are commonly 

 met with. A notable example is the occurrence of guano 

 at Olsen's Caves, near Rockhampton, in Central Queensland. 



To summarise, phosphate deposits may occur in Aus- 

 tralia, 



F — Royal Society. 



