440 Transactions. — Geology. 



being evidently derived from the Tairua andesitic tuffs. The 

 masses generally present a corroded and often ropy appear- 

 ance, with a pitted surface. Under the microscope it is seen 

 to consist of a very pale-yellow glassy ground-mass, with 

 scattered feldspars and augite, the former occurring as narrow 

 laths and phenocrysts, apparently representing two crops of 

 generation. The feldspar laths are arranged with their 

 principal axes parallel to the fluxion plane. Some binary 

 twins do not exhibit straight extinction, and cannot be 

 sanidine. The majority of the feldspar microliths and plates 

 appear to be plagioclase. Augite is fairly abundant, often 

 well formed and generally twinned. Occurs both as plates 

 and narrow laths, which lie with their long axes parallel with 

 the fluxion plane. Polarisation colours very brilliant. One 

 phenocryst,'showing multiple twinning, encloses two crystals 

 of feldspar. Magnetite not very abundant. 



Andesitic Glass, Omahu Hild. 

 This is a black semi-vitreous rock speckled with white 

 feldspars. Lustre vitreous ; feels rough. It occurs as irregu- 

 lar masses in the grey tuffs on the Omahu Bridle-track, about 

 a quarter of a mile on the Thames Valley side of Odlam's 

 gold-mining claim. Under the microscope it is seen to con- 

 sist of a grey glass exhibiting wavy fluxion lines, and sur- 

 rounding a few large and badly developed phenocrysts of 

 plagioclase. Some patches of the base are partially devitri- 

 fied and crowded with microliths of feldspar and augite. 

 Augite is fairly abundant. A little magnetite is dusted 

 throughout the base. 



Art. XLI. — On the Secular Movements of the New Zealand 



Coast-line. 



By Professor James Park, F.G.S., Director, Otago University 



School of Mines. 



[Read before the Otago Institute, 12th November, 1901.] 



The solid ground is popularly considered the symbol of 

 stability, but exact observations in the older-peopled countries 

 of Europe have shown that, on the contrary, the crust 

 of the earth is in a state of constant oscillation. The 

 upheaval or depression of the land from this secular move- 

 ment is so slow and gradual as to produce no appreciable 

 difference in the physical aspect of the ground affected from 

 year to year, and it is only after the lapse of generations, and 



