130 Transactions. 



phenocryst the grouudmass shows correspondingly less of that mineral. 

 It is sometimes so coarse that the rocks then deserve to be classed as 

 granite-porphyry. 



In one section there are a few spongy crystals of brown hornblende, 

 which enclose several quartz-grains ; in the same section there is a xenolite 

 which is apparently a fine weathered granodiorite. 



Granophyre. (Plate XXVIII, fig. 3.) 



This rock has occasional fairly coarse idiomorphic phenocrysts of plagio- 

 clase in a groundmass which contains a moderate amount of plagioclase in 

 laths enwrapped pseud o-poecilitically by quartz crystals which sometimes 

 are large. A very great portion of the matrix, however, consists of micro- 

 pegmatite, as is well exemplified by fig. 4, Plate XXVIII. There are a few 

 minute flakes of greenish-brown biotite. 



The occurrence of granophyres in New Zealand is rather limited. Sollas 

 and McKay (1906, vol. 2, p. 182) describe them from a conglomerate 

 outcropping on the east shore of Palliser Bay, near Wellington. A rock 

 collected by Smith (1908) from river-gravels in Westland, and described 

 by him as granite-porphyry, seems equally to merit the name " spherulitic 

 granophyre." 



(?) Tufaceous Acidic Rock. 



A difficult rock to classify. It is decidedly fragmental in general character, 

 but appears to have the fragments enclosed in a matrix which is unlike 

 that of a tuff. It is a finely granular mixture of feldspar, green hornblende, 

 and probably quartz, with frequent spherulitic and micropegmatitic inter- 

 growths (see photomicrograph, Plate XXVIII, fig. 5). In it there are large 

 broken crystals of plagioclase, a few of orthoclase, many coarse ones of quartz, 

 and some biotites which are generally chloritized. There are also very small 

 fragments of finely micropegmatitic material, of very fine-grained andesites 

 (some with a little green hornblende), and of an exceedingly fine-grained 

 rock made up of green hornblende and feldspar along with a little 

 micropegmatite and probably quartz. 



An interesting phenomenon is the enclosure of micropegmatite and of 

 some of this last-mentioned rock by quartz crystals. In some instances 

 (see Plate XXVIII. fig. 6) there is a very definite band-like margin to the 

 inclusions. 



These inclusions, and the nature of the matrix, furnish grounds for 

 suspecting that the rock is not a txiff, but an intrusive in which fragments 

 of intruded rocks have been entangled. Marginal resorption could readily 

 explain the rounded forms of the rock-fragments. 



Andesitic Tuff. 



This is a compact fine-grained rock having an andesitic matrix in 

 which are enclosed small particles of very fine-grained trachytic rock, either 

 trachyte or trachyandesite. 



References. 



Bartrum, J. A., 1920. The Conglomerate at Albany, Lucas Creek, Waitemata Harbour, 



Trans. N.Z. Inst., vol. 52, pp. 422-30. 

 Bell, J. M., and Clarke, E. de C, 1909. The Geology of the Whangaroa Subdivision, 



N.Z. Geol. Surv. Bull. No. 8 (n.s.). 

 Smith, J. P., 1908. Some Alkaline and Nepheline Rocks from Westland, Trans. N.Z. 



Inst., vol. 40, pp. 122-37. 

 Sollas, W. J., and McKay, A., 1906. The Rocks of Cape Colville Peninsula. 



