"Vol. 65.] AND MAGNESIAN ROCKS OF NEW ZEALAND. 355 



Longitudinal sections show further the cross-fractures which are so 

 marked in the hand-specimen. 



It appears that we are here dealing with a differentiated intru- 

 sion of peridotites, which were accompanied by emanations of boron 

 compounds, an unusual feature in this class of rock. Hydration of 

 the minerals has occurred, followed by considerable dynamic stress, 

 which has left its effects on the tourmaline crystals and on the more 

 foliated portions of the intrusion. There is no doubt, then, that 

 the intrusion antedates the period of general metamorphism of the 

 surrounding schists and quartzites. 



(2) Dun Mountain. 



The rocks here described consist of an intrusion 6 miles south 

 of the town of Nelson, having an average width of 3 miles. The 

 intruded rocks are indurated breccias and red and green slates 

 on the south-east side, and Maitai limestones and slates on the 

 north-west. The former have been classed as Devonian and the 

 latter as Carboniferous [19] ; but for this correlation there is 

 scant evidence, and the recent researches of Prof. Park indicate 

 that the rocks are of either Triassic or Jurassic age [20]. The 

 boundary of the magnesian rocks is particularly well marked by 

 the sudden change from thick bush on the calcareous slates and 

 limestones to bare tussock-covered or rocky slopes when passing on 

 to the serpentines and peridotites. The description of two sections 

 across the intrusion will indicate sufficiently the character of the 

 rocks. 



Section 1 (Aniseed Valley). — In this line ot section (fig. 2, 

 p. 356) the Maitai rocks on the north-west side, striking north to 

 north-east, and standing vertically or dipping very steeply away from 

 the intrusion, are dark slates of varying texture, with bands of 

 limestone bordering the intrusion. The limestones are succeeded 

 by a belt from 50 to 100 yards wide of a mottled rock composed, as 

 Prof. Marshall has pointed out, of the lime-garnet grossularite with 

 diallage, and evidently formed by contact-metamorphism of the 

 limestone. Passing up the valley, this contact-zone is succeeded 

 by a wide belt of rocks composed largely of serpentine, either dark 

 and massive or paler and foliated. The former variety is veined 

 with fine chrysotile, while the leek-green foliated belts of serpentine 

 carry occasional picrolite (columnar serpentine) on selvages. Asso- 

 ciated with the serpentine are bands of pyroxenite (diallage-rock) 

 of all degrees of coarseness, and small veins of saussurite-gabbro, 

 highly serpentinized olivine-gabbro, and dunite. Veins of both 

 grossularite and wollastonite occur as products of contact- 

 metamorphism, scattered through the serpentine ; and a prominent 

 belt of copper and other sulphide-ores occurs in the serpentine near 

 the contact-zone. On the other side of the intrusion the serpentine 



