Hamilton. — Geology of Bluff District. 453 



hill; but as soon as the range trends to the north, the outlying 

 dykes strike still parallel to the base of the hill, but almost at 

 right angles to the strike of the slates, cutting them trans- 

 versely, and crumpling and contorting them in every conceivable 

 way, just as a wedge driven into wood transverse to the fibre 

 would bend and crumple the parted ends towards the right or 

 left. Many instances of this are seen where the slate beds are 

 cut at different angles by dykes of syenite, or diorite, from 4 to 

 20 feet thick, and bent by the intrusion of the latter sidewise in 

 curves, in some instances almost semicircular. 



In the debris of these dykes I found two large crystals, appa- 

 rently of amphibole ; one a thick hexagonal prism about 

 7 inches long, and as much or more in circumference, dark 

 greenish- grey, and rough on the faces ; the other about 4 inches 

 long, also hexagonal, but instead of ending in a pyramid its ends 

 consisted of only two planes meeting at an angle of about 60°, 

 but I did not measure it, intending to examine it more care- 

 fully at home. This, unfortunately, I was precluded from doing. 

 As they were somewhat heavy to carry, and I had a day's walk 

 before me, I put them aside, meauiug to get them on my way 

 home. On my return the tide had risen higher than my calcu- 

 lations, and had taken temporary charge of my crystals ; and 

 notwithstanding that I have twice sought for them since, I have 

 not been able to pick them up again. 



In these dykes also blade-like crystallizations are not rare, 

 of large size, and sometimes ending in an imperfectly-shaped 

 four-sided pyramid. Small rough crystals are also frequently 

 observable of undoubted hornblende or augite. All these could 

 not have been the result of metamorphism, and prove conclu- 

 sively that the range itself, of which these are but the outliers, 

 must be a truly instrusive mass. 



The age of the syenite, or, in other words, the period of 

 intrusion, is the next question : and this can only be inferred 

 from the characters of the rock itself. In many respects these 

 are quite peculiar. It is heavily charged with sulphides and 

 bisulphides, and so full of magnetite that a piece of the size of 

 the hand will, in many cases, deflect the compass-needle 8^ or 

 10°. The whole mountain is an immense magnet ; and, in 

 walking over it, the needle is constantly varying both in declina- 

 tion and dip. Iron is therefore present in far larger quantity 

 than is usual in ordinary granitic rocks. Copper is present in 

 every specimen I have tested, and often in considerable quantity. 

 It is not at all improbable that a workable lode may yet be 

 found of this metal at some of the points of junction with the 

 slate. Manganese occurs plentifully in the detritus on the 

 shore, from the wearing down of the rock by the sea. Black 

 ironsand, auriferous and platiniferous, occurs under the same 

 conditions so plentifully that it has been profitably washed for 



