Marshall. — Nephelinite Socks in New Zealand . 



307 



The Auckland type is somewhat similar to that of Omimi (analysis D). 

 In most specimens the large augites have an ophitic structure. The 

 olivine crystals, again, have a great length, 1-5 cm. by 0-46 mm., and again 

 the direction of elongation is that of the axis a. The intergrowth of 

 augite and nepheline is very complete, but is not carried to the extent of 

 excessive fineness that is found in the Omimi type. The groundmass is 

 rather more plentiful, and contains aegerine, apatite, and feldspar. 



This rock is associated with basaltoid lavas which contain very little 

 nepheline. The numerous volcanic cones near Auckland are formed of 

 this dense type of basanite. The Auckland rocks have been mentioned 

 previously (Marshall, 8). 



Chemically, as would be expected, all the rocks mentioned are closely 

 related, as is clearly shows by the following analyses : — 



A. Coarse nephelinite, Lake Waihola. 



B. Fine nephelinite, Clarendon. 



C. Finest type of nephelinite, Clarendon. Andrew, Trans. N.Z. Inst., 

 vol. 38 (1906), p. 461. 



D. Nephelinite with micrographic structure, Omimi. 



E. Nephelinite with micrographic structure, Auckland. 



F. Nephelinite, Regatta Point, Tasmania. Paul, Tscher. Mitt., bd. 25 

 (1906), p. 301. 



Literature. 



1. Hutton, F. W. " Geology of Otago," p. 56. Dunedin, 1875. 



2. Hutton, F. W. " The Eruptive Rocks of New Zealand." Proc. 

 Roy. Soc. N.S.W., 1889, p. 134. 



3. Ulrich, G. H. F. ; " On the Occurrence of Nepheline-bearing Rocks 

 in New Zealand." Trans. Aust. Ass. Adv. Sci., vol. 11 (1907), p. 127. 



4. Andrew, A. R. " On the Geology of the Clarendon Phosphate- 

 deposits, Otago, New Zealand." Trans. N.Z. Inst., vol. 38 (1906), p. 461. 



5. Marshall, P. "The Geology of Dunedin, New Zealand." Quart.. 

 Jour. Geol. Soc, vol. 62 (1906), p. 381. 



6. Paul, F. P. " Beitrage zur petrographischen Kenntniss einiger 

 Foyaitisch theralitischer Gesteine aus Tasmania." Tscher. Min. Pet. 

 Mitt., bd. 25, heft 4 (1906), p. 301. 



7. Marshall, P. " Trachydolerites near Dunedin." Trans. Aust. Ass. 

 Adv. Sci., vol. 10 (1904), p. 183. 



8. Marshall, P. " Distribution of the Igneous Rocks of New Zealand." 

 Trans. Aust. Ass. Adv. Sci., vol. 11 (1907), p. 366. 



