Bartrum. — The Distribution of Igneous Rocks in New Zealand. 421 



at all events, crystallized out during the solidification of the magma, pro- 

 bably largely at the expense of unstable hornblende. It is shown by the 

 figure, which represents one of several similar examples, that, on occasion 

 at all events, the epidote is one of the earlier products of crystallization. 

 A twin crystal of it here surrounds a central twin crystal of idiomorphic 

 hornblende ; it encloses a few flakes of biotite, and is itself enwrapped by 

 biotite and plagioclase. A very narrow partial border to the hornblende 

 (exaggerated in the figure) is possibly also epidote. 



It seems impossible to escape from the conclusion that the relations of 

 mineral to mineral establish the primary character of at least some of the 

 epidote. Such epidote is not unknown, but it does not seem commonly 

 to have been described.* 



Basalt with Biotite (Var. ? Anomite), South of Tokatoka Swamp, 



Wairoa River. 



This is the stone often used in Auckland for monumental work, and called 

 locally the " Kaipara granite." The writer has examined this and several 

 other of the Kaipara extrusive and intrusive rocks and has found them 

 mainly normal basalts, but there are also andesites such as that at Toka- 

 toka, near Dargaville, which carries a deep-green hornblende. 



The " Kaipara granite " is a very coarse-grained basalt with abundant 

 coarse olivine, enclosed with plentiful pale-green augite and coarse ilmenite 

 in a coarsely pilotaxitic holocrystalline feldspathic groundmass. 



The point of interest about the rock is that it contains a highly pleo- 

 chroic (rich reddish-brown to pale canary-yellow) biotite in abundant flakes 

 which are often sharply euhedral. In one or two instances these enclose 

 ophitically the feldspar of the groundmass. 



The optic axial angle in the few favourable sections obtained varies 

 from zero to a few degrees, the biaxial character being distinct in only one 

 instance. The dispersion for red is greater than that for the blue rays. 

 The pleochroism is Y = Z = rich reddish brown, X = pale canary -yellow or 

 golden. 



This mineral is similar to a biotite in basanites near Dunedin which 

 Professor P. Marshall first showed me in 1907, and which he considered 

 anomite. The characters of the biotite in the Kaipara rock, so far as they 

 are determinable, agree with those given by Rosenbusch for anomite. f 



Sollas has described a biotite basalt from a Tertiary conglomerate at 

 the Waipaoa River, Poverty Bay,J whilst Andrew has discovered anomite 

 in a similar rock near Milburn, 6tago.§ 



Hornblende Basalt, Sumner-Lyttelton Road, near Sumner. 



Marshall has mentioned the occurrence of hornblende basalts at Dun- 

 edin, j| but, apart from these, few hornblende basalts seem to have been 

 noted from New Zealand. 



* See, for example, H. Rosenbusch, Mikroskcpische Physiographie, 4th ed., i, 2, 

 1905, p. 284 ; and E. WeINSCHENK (trans, by R. W. (lark), Petrographic Methods, 

 1912, pp. 264-65. 



t H. Rosenbusch, he. cit., pp. 259-60. 



I W. J. Sollas and A. McKay, Rocks of Cape Colville Peninsula. Wellington 

 Government Printer, vol. 2, 1906. p. 176. 



§ A. R. Andrew, On the Geology of the Clarendon Phosphate -deposits, Otago, 

 New Zealand, Trans. N.Z. Inst., vol. 38, 1906, p. 459. 



|| P. Marshall. The Geologv of Dunedin (New Zealand), Quart. Journ. Geol. Soc. 

 vol. 62, 1906, p. 412. 



