365 



passage from forms allied to the South American types, to those of the 

 Australian seas. 



The occurrence of Secondary Cephalopods and Saurian reptiles in the 

 lower groups renders it probable that the strata range from Jurassic formations 

 upwards. But this is a subject pertaining purely to geology. 



I will next proceed to describe briefly the Igneous rocks found in these 

 islands, some of which have a more direct relation to the presence or absence 

 of minerals than any of the foregoing. 



Among the crystalline rocks we find Syenites, and many varieties of 

 Hornblende and other basic rocks, but they are chiefly to be considered as 

 varieties of metamorphic rocks. In the great Schistose area of Otago, there 

 is a very marked absence of all Igneous rocks, except towards the eastern border, 

 where Dolerites, belonging to the Miocene period, have escaped tlrrough the 

 Schists at a few points, but without influencing their mineralogical character. 



It is not till the period of the lower Mesozoic rocks, previous to the break 

 in the geological sequence which I have described, that any contemporaneous 

 Igneous formations have been detected. These consist of Diorites, Diabase, 

 and Porphyries, associated with mechanically-formed strata of the same 

 materials (Diorite sandstones and Breccias), containing fossils that indicate the 

 period to which they belong. This formation is associated with a variety of 

 altered rocks, of which Serpentine is the most prominent, and on the whole 

 closely resembles in character the Diorite formation of South America, as de- 

 scribed by Darwin and David Forbes. These Diorite rocks are found along a 

 line that extends almost continuously through the South Island, chiefly along 

 the western slope of the mountain axis, but they also appear in one or two 

 localities on the eastern side of the range, though there presenting somewhat 

 different characters. As the best known example of this formation I may 

 instance the Dun Mountain, and mineral belt of Nelson. 



What I take to be the same formation occurs in the North Island among 

 the older rocks of the Colville peninsula, Barrier Island, and other mining 

 districts. The relative date of the different Igneous rocks, subsequent to the 

 foregoing, can generally be determined with considerably certainty. They 

 present great variety, and belong chiefly to the upper Tertiary period, but it 

 will be found, as our observations are extended, that volcanic outbursts were 

 taking place in the New Zealand area, at almost every period subsequent to 

 the Mesozoic Diorite series. The influence of the more modern volcanic rocks 

 in producing mineral lodes and veins has been very slight, the only well- 

 established cases being when they have been erupted through the Igneous 

 rocks of the Diorite group, as at Coromandel and the Thames. 



Keeping clearly before us these leading characteristics of the geological 

 structure of New Zealand, it is highly interesting to compare them with the 

 structure of the nearest large mass of land in Australia. 



Extending along the eastern border of the Australian continent, we have 

 within a short distance of the coast the Australian Cordillera, a main range of 

 Primary iTtcks, flanked on the east side by a shelf-like remnant of Secondary 

 strata, comprising the various coal fields of New South Wales, while on 

 the west side is an expanse of low-lying country, where only very modern 

 Tertiary formations are found. Towards the South end of the range in 

 Gippsland, we have masses of granite lying to the west of an area of Mica 

 slate and other metamorphic rocks. The mai-ked resemblance of the natural 

 features of this district to the Otago province of New Zealand has been 

 frequently mentioned by diggers, while the analogy of geological structure in 

 the two districts has been the subject of correspondence between Mr. Selwyn, 

 the late Government geologist of Victoria, and myself. Now I find that by 

 covering the Australian Cordillera in a map of Australia, with a tracing of 



