ROCK PHOSPHATES OP S. AUSTRALIA. 2:43 



Cambrian limestone, which occupies the higher ground, and forms the 

 hillj country extending from this place to Pekina Creek. The strike 

 of the rocks' is north-north-easterly, and the dip generally more or less 

 vertical owing to extensive denudation acting on anticlinal and syji- 

 clin^l folds. 



The phosphate rock deposits, so far as they have been tracetl 

 downward, some 20 ft. or so, appear to be roughly interstratified with 

 the rocks in which they occur, and also partake of the nature of lode 

 formations, particularly near the outcrops. 



Numerous other deposits exist, and the occurrence of rock phos- 

 phate, at intervals, has been demonstrated for about 200 miles along 

 the Main Range; but the chief characteristics of the most important 

 deposits have now been given, and it is not necessary to go into further 

 descriptive detail. 



These deposits are already of economic value, about 24,000 tons 

 of crude rock having been marketed during the six years which have 

 elapsed since the first discovery; they are not yet able, however, to 

 successfully compete with the imported rock from Christmas and Ocean 

 Islands, but I feel assured that we may with every confidence look 

 forward to the time when they will be of the greatest importance and 

 value, not only to the State of South Australia, but to the Common- 

 wealth generally. 



Suggested Origin. 



A special feature in connection with some of these rock phosphate 

 occurrences is their (apparent) bedded character and interstratification 

 with soft earthy argillaceous and arenaceous and calcareous beds, 

 which are interstratified with the Cambrian limestones, quartzites, 

 sandstones, and other rocks belonging to that series. This is accom- 

 panied by evidences of segregations of phosphate as bands and nodular 

 masses in clay and argillaceous material derived from the disintegra- 

 tion of the soft rocks above mentioned. Quartz as small veins, oxides 

 of iron and manganese, are associated in all localities hitherto dis- 

 covered, indicating to my mind deposition by solution from phosphate- 

 bearing rocks in a similar manner to what is supposed to occur in the 

 formation of lodes. 



A theory that may be put forward to account for the bedded 

 character of the deposits is that during the time the Cambrian rocks 

 were deposited, the mud and other argillaceous and arenaceous beds of 

 the then existing sea-bottom were inhabited to a greater or less extent 

 by forms of life which secreted phosphate matter and phosphate of 

 lime, as carbonate of lime was secreted by the coral animalcules which 

 are responsible for the deposition of the limestone : that in the argil- 

 laceous deposits these phosphatic animalcules were developed in larger 

 proportion than in the limestone, in which latter animalcules secreting 

 carbonate of lime were in the majority, probably because such material 

 was more favourable to their existence. Phosphate of lime may also 

 have been derived from the coverings of a few of the Brachiopoda, 

 such as Lingula and its allies, and from some of the Trilobites. 



