492 Transactions. 



Remarks on Stratigraphy. 



From the above description, the matrix of the Kakanui 

 " gem gravels " is seen to be a submarine volcanic breccia oc- 

 curring on or near the sea-coast at the mouth of the Kakanui 

 River. It is covered in all exposures by a limestone having the 

 same nature and bearing the same fossils as the Ototara lime- 

 stone, so that its stratigraphical position is in the Oamaru 

 system. From the nature of the fossils in the breccia, and the 

 occurrence of glauconite in and above the limestone, the forma- 

 tion of the breccia must have taken place at a considerable depth 

 below sea-level. Should this breccia prove to be a matrix for 

 gems, there would be three or four exposures where it might be 

 quarried, and a surface-area of some acres. As there must have 

 been one or more craters from which the breccia was erupted, 

 there must be pipes running down to a considerable depth, and 

 most likely containing larger fragments of mineral and less 

 calcite. These could be worked by mining, although the per- 

 meable nature of the breccia might allow of a large influx of 

 water. Should gems occur, they would probably be of a suffi- 

 cient size in these pipes to repay working. 



Identifications of the Minerals and Rocks contained in 



the Breccia. 

 Complete and detailed descriptions of these minerals will 

 be of considerable petrological interest, but are withheld till 

 further work has been done. It will be sufficient here to state 

 that, after a considerable amount of chemical and microscopic 

 examination, the following were identified : — 



Black augite ] 



Hornblende - in large fragments. 



Feldspar, near oligoclase ) 



Garnet 



Diopside 



Diallaee • n <■ 



T3- - in smaller Irasmients. 



Biotite 



Olivine 



Smaragdite 



Basalts. 



Sandstone, limestone, greywacke. 



Quartz, mica-schist, granulite, and garnet gneiss. 



Various basic plutonic rocks, which may be grouped in 

 two classes — (1) lherzolites, eulvsites, and wehrlite 

 (containing fine spinels) ; (2) garnetiferous peridotites. 



The basalt contains inclusions of almost all the other rocks 

 and minerals found in the breccia. 



