Thomson. — The Gem Gravels of Kakanui. 483 



their matrix there has been occasion to make some general 

 remarks on the geology of the district. For the purposes of 

 more convenient reference hereafter, it has been thought desirable 

 to keep detailed descriptions of the collected fossils for a separate 

 paper. 



Kakanui (Maori; "large kaka ") is the name of a range of. 

 mountains, a river, and a township, all situated in the north- 

 oast corner of Otago. The name has been applied by Captain 

 Hutton to the upper part of the Wanaka system, of early 

 Palaeozoic age, typically developed in the Kakanui Mountains. 

 The Kakanui River derives its gravels largely from these and 

 younger submetamorphic rocks. The country between the river 

 and the sea is composed mostly of the Oamaru formation of early 

 Tertiary age. It may be roughly described as consisting inland 

 of conglomerates overlaid by limestones, near the coast of ash- 

 beds capped by limestones. 



Previous Observers. 



There appears to be no reference, in the many geological 

 papers dealing with the neighbourhood, bearing directly on the 

 " gem gravels " as such. The Oamaru district is the typical 

 locality for the Oamaru system in New Zealand geology, and 

 has been frequently explored by geologists, chiefly for the sake 

 of determining the age of the system (which by Sir James Hector 

 is included in his Cretaceo-tertiary system, and by Captain 

 Hutton is ascribed to Oligocene). The papers on this subject 

 occur mostly in the " Reports of the Geological Survey of New 

 Zealand " and the " Transactions of the New Zealand Institute." 

 These will be referred to in due place. 



Mr. Mantell, the first geologist to visit the district, noted the 

 " volcanic grit " of Kakanui, which has proved to be the matrix 

 of the " gem sands." His observations on these minerals seem 

 to have been entirely overlooked by all subsequent observers, 

 although his paper is frequently referred to in discussions on 

 the age of the rocks. The following is the paragraph referred 

 to : " The volcanic grit of Kakanui . . . contains a great 

 variety of crystalline volcanic products, as hornblende, augite, 

 garnets, &c." * 



After the fullest inquiries from residents in the district, and 

 personal examination of many localities, both in the vallevs of 

 the Kakanui River and its tributary the Waiareka, it has been 

 found that there are three distinct occurrences of stones that 

 may be possibly of value as gems. The first is of sapphire, 



* Mantell, Quart. Journ. Geol. Soc, 1850, p. 325. 



