34 Transactions. 



Part I. — Parapara, Nelson. 



The authors of Bulletin No. 3 of the Geological Survey describe certain 

 basic facies of the Waitapu granite as occurring only at the contact with the 

 carbonate rocks, and are led to the conclusion that it was owing to the in- 

 troduction of the carbonate bases into the acid magma that these basic 

 facies arose. This theory of assimilation or absorption has its home in 

 France, and its most notable protagonists in Levy* and Lacroix.f It 

 receives support from Finnish geologists, but is strongly opposed by the 

 differentiation school of Rosenbusch and Brogger, with whom English petro- 

 logists are in large part inclined to agree. In America, however, the French 

 have a strong following. J 



One of the difficulties in settling the question is the rugged and inacces- 

 sible nature of the country in Ariege described by Lacroix, while another lies 

 in the complication of phenomena in regions of crystalline schists such as 

 Adams describes. It suggested itself to me that the Parapara district would 

 furnish an excellent case on which to test the rival theories, and Dr. Bell, 

 Director of the Geological Survey, kindly furnished me with six specimens 

 for preliminary study. These will now be described in detail. 



The members of the igneous complex are represented by an acid and a 

 basic type. The acid rock has the structure of an augen-gneiss and the 

 mineral composition of a binary granite. The feldspars, which form the 

 augen, are mostly untwinned and partially sericitised, and are referred to 

 orthoclase, but there are also present microcline, and albite in microcline- 

 microperthite. Graphic intergrowths of quartz and orthoclase are fairly 

 abundant. Both dark and white mica are arranged in parallel flakes along 

 the planes of foliation, the former in course of alteration to chlorite and 

 rutile. Apatite is not abundant, but magnetite is more plentiful, and it is 

 evident that the original iron-ore was titaniferous, since the magnetite 

 shows minute outgrowths of a highly refringent platy mineral determined 

 as anatase. There is, in addition, a brown mineral of which only one large 

 prismatic crystal appears in the section, with a pleochroism from brown to 

 yellow. The orientation is not favourable for study in convergent light, 

 and the mineral is doubtfully referred to cero-epidote on account of its low 

 obliquity of extinction. Although it is paler in colour than is usual in com- 

 mon orthite, it is too pleochroic for monazite. 



The basic rock shows, in section, abundant common hornblende 

 enveloping colourless patches, which are evidently pseudomorphs after 

 feldspar. They consist chiefly of muscovite and epidote, but a little 

 basic plagioclase has here and there escaped alteration. Magnetite is 

 probably an original constituent, but much of the iron is now present as 

 pyrite. 



Secondary alterations in the large hornblende plates are of two kinds : 

 there is a decomposition to clinochlore and sphene, to be ascribed to shallow- 

 seated alteration, and also a local separation of minute needles of rutile and 



* Levy, MM. " Le granite de Flamandville, &c.," Bull. Carte geol. Fr., tome v. 

 No. 36, 1893-4. " Sur revolution des magmas de certains granites a amphibole," Comptes 

 Rcndus. cxxi, p. 228, 1895. " Sur quelques partioularites de gisement du porpliyi-e bleu 

 de I'Esterel," Bull. Soc. geol. Fr., 3rd ser., xxiv, p. 123, 1896. 



t Lacroix, A. " Les granites des Pyrenees et leur phenomenes de contact." Bull. 

 Carte geol. Fr., tome x, No. 64. 1898-99. 



% Cf. Adams, F. D., on the Structure and Relations of the Laurentian System in 

 Eastern Canada. Q.J.C4,S., Ixiv, pp. 127-47. 1908. 



