Academy of Sciences] 

 No. 1] 



AUSTRALASIA. 



43 



fully investigated mass of serpentine occurs. It commences in D'Urville Island and continues 

 intermittenly for many miles to the south-southwest, parallel to the general strike of the invaded 

 Paleozoic and Mesozoic sediments. The most continuous patch includes the Dun Mountain, 

 and extends for nearly 20 miles. 5 Its irregular outline suggests that it was formed by a series 

 of coalescent sill-like intrusions of peridotite, now serpentinized associated with a little "rod- 

 ingite" or grossularite-gabbro. (Marshall '11.) (Fig. 13.) While the general extension of the 

 mass is thus concordant, the boundaries considered in detail usually transgress the bedding- 

 planes of the invaded formation. The majority of the exposed rock is serpentine; harzbergite 

 is common, but its distribution relative to that of the dunite has not yet been studied in detail. 

 The dunite not infrequently contains a small amount of pyroxene, and the chromite is dis- 



FlQ. 13.— Geological map of the Dun Mountain District, New Zealand. (After Marshall and others.) 



1. Alluvium. 



2. Tertiary. 



3. Rodingite. 



4. Peridotite and serpentine. 



5. Mesozoic (?) basalts, etc. 



6. Mesozoic and Permian greywackes. 



7. Permian limestone. 



8. Fault-lines. 



tributed somewhat streakily in it. Strain-phenomena are common in the crystals, but there is 

 not an excessive amount of crushing. Masses of very coarse grained websterite also are present. 

 The rodingite has been rightly compared with the garnet-rocks in New South Wales mentioned 

 above, but in the writer's view (Benson '13, pp. 684-689, '18, p. 722) neither should be considered 

 primary magmatic crystallizations, but produced secondarily, probably largely through the 

 action of the concentrated magmatic water. Long sill-like masses of serpentine occur also in 

 the Collingwood (Takaka) region to the northwest from Dun Mountain (Bell '07), where they 

 form lenticular masses elongated parallel to the nearly meridional strike of the invaded Ordovi- 

 cian sediments against which the granite has strongly transgressive boundaries. Serpentines, 

 often antigoritic, again form a group of narrow sills, rarely more than a mile in length, in the 

 steeply folded schists and phyllites to the east of Hokitika (Bell '06), and similarly occur in the 



• This is the occurrence whence the typical dunite was first obtained by Hochstetter (65) in 1859. 

 81795°— 26 i 



