WoRLEY. — Oil the Geology of Nelson. 417 



Leaving Wairoa Gorge, and travelling up Aniseed Valley, a 

 still older series of rocks is met with. These rocks are known 

 as the Maitai slates, and form part of a very extensive system, 

 known to geologists as the Carboniferous system. These 

 slates, in the lower part of the valley, consist of fine-grained 

 clay-slates. Further up the valley the slates become cal- 

 careous ; and finally a magnificent belt of mountain limestone 

 is reached. This limestone, and the slates already mentioned, 

 are the principal rocks of the Carboniferous system. These 

 rocks are very extensive, and form the greater part of the 

 mountain-chains of the district. They pass from end to end 

 of the provincial district, forming part of the Spenser Moun- 

 tains, St. Arnaud Mountains, and the low^ mountain-range 

 running from the St. Arnaud to the Pelorus Sound. As off- 

 shoots from the main range they reach almost to the Town of 

 Nelson — Fringe Hill and Botanical Hill being composed of 

 this rock. Extending from Mount Franklyn to D'Urville 

 Island, and running in the same direction as the mountain 

 limestone and the Maitai slates, is a stretch of country known 

 as the "mineral belt." This formation presents a marked con- 

 trast to the limestone and slates of the Carboniferous forma- 

 tion. The latter are covered with dense bush, having a 

 luxuriant undergrowth, but, when the mineral ground is 

 reached, the bush terminates abruptly, and gives place to a 

 succession of bare hills, whose rugged gi-andeur cannot fail to 

 impress the least observant. The lithological character of the 

 rocks is also strikingly different. Instead of regularly-strati- 

 fied rocks, such as are found in the Port Hills, the Wairoa 

 series, and the Maitai series, we have masses of dark horn- 

 blendic rocks, diorite, serpentine, and dunite. Dunite, the 

 tj'pical rock of the Dun Mountain, is an olivine rock con- 

 taining traces of chromium. The rock itself is crystalline, 

 and of a yellowish-green colour ; but where exposed to the 

 weather its hue has changed to a rusty-brown ; hence its 

 appropriate name, dunite. It is this formation that contains 

 the deposits of copper and chrome to which I shall refer 

 more fully when dealing with the economic minerals of the 

 district. 



Eeference has already been made to the mountain-forming 

 character of the Maitai slates and the underlying Carboniferous 

 limestone. I shall now attempt to describe how these rocks 

 were formed, and how they came into their present position. 

 Limestone, as most of you are aware, is of organic origin. 

 Carbonate of lime exists in solution in sea-water. Certain 

 marine animals have the power of extracting the carbonate of 

 lime from the sea-water and of converting it into a solid sub- 

 stance, which they use as a protection or covering for their 

 bodies. "When these animals die the shells in which they 

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