76 ORIGIN AND OCCURRENCES OF PHOSPHATE ROCK 



{a) as apatite in very old schist and gneiss formations 

 that have been intruded by basic igneous rocks. 



{b) as phosphorite in paloeozoic limestones, where 

 unconformities occur above them, and leaching 

 by subaerial agencies may have taken place. 



(c) as phosphorite in Tertiary limestones, where 

 animals have died in large numbers on the 

 desiccation of our interior in Pleistocene times. 

 Such occurrences might be met with in Central 

 Australia, and round the shores of the Aus- 

 tralian Bight and the Gulf of Carpentaria. 



{d) as bone breccia in limestone caves. 



(e) as guano deposits in limestone caves. 



