Andrew. — On the Clarendon Phosphate-deposits. 447 



Art. LIT.— On the Geology of the Clarendon Phosphate-deposits. 



Otago, Neiv Zealand. 



By Arthur E. Andrew, B.Sc, A.O.S.M., Laboratory, Otago 

 University School of Mines. 



Communicated by Professor James Park. 



[Read before the Otago Institute, 8th August, 1905.] 



Plates IV- VIII. 



Introductory. 



The Limestone Quarries. — The Millburn district is well known 

 throughout Otago by reason of its deposits of limestone, which 

 have now been worked for more than thirty years. Numerous 

 quarries have been opened up in various parts of the district, 

 but there are only two in active operation at present — that of 

 the Millburn Lime and Cement Company, near the Millburn 

 Railway-station, and Wilson's quarry, close to the main road 

 and about half a mile north of Millburn. The lime derived 

 from the burning of the limestone is for the most part used for 

 agricultural purposes, the Millburn Company alone producing 

 lime suitable for building. The company has large works at 

 Duneclin, and send there by rail all the lime they require for 

 making cement ; " land lime " nevertheless constitutes the bulk 

 of their output. I understand that this company has been 

 considering the possibility of using their limestone in the manu- 

 facture of calcium-carbide. As will be noted below, some of 

 the limestone in their quarry contains a small amount of phos- 

 phoric acid, and in quarrying great care will be needed lest any 

 of this stone should be sent to the carbide-works. In the manu- 

 facture of calcium-carbide from limestone, any phosphorus pre- 

 sent associates with the carbide, and, when the latter is acted 

 on by water to generate acetylene, forms compounds which 

 mingle with the gas and burn with the production of a most 

 disagreeable odour. The limestone is not used as a building- 

 stone, as it is broken up into small blocks by the planes of lami- 

 nation, stratification, and jointing, which are well defined and 

 set close together. 



Other Workings. — Other rocks in the district are also of 

 economic importance, though in a less degree. The schist 

 which forms the floor on which the later deposits were laid 

 down is occasionally used for building walls and fences — a 

 purpose for which its flaggy nature renders it suitable. The 

 basalt which forms the cap of the hills is quarried and used 



