Hutton. — On some Ancient Bht/olites. 269 



Brunner Coal series, at the place where the Davy Mountains 

 reach the sea ;* and the short examination I made of the Grey- 

 mouth District quite bears out his views, although I did not go 

 so far as Mount Davy. 



Art. XXXIV. — On some Ancient Rhyolites from the Mataura 



District. 



By Professor F. W. Hutton, F.G.S. 



[Read before the Philosophical Institute of Canterbtiry, &th October, 1887.] 



These rocks were collected by M. Gordon Bich, Esq., near 

 Waipapa Point, east of the mouth of the Mataura. They occur 

 as more or less rounded boulders, and with them are found por- 

 tions of silicified tree-fern stems, and of beautifully preserved 

 coniferous wood, all of which probably came down the Mataura 

 River. The vegetable remains come no doubt from the Hokonui 

 System, and probably the rhyolitic rocks accompanying them 

 are of the same age, or not much older. At any rate they are 

 of considerable interest as showing that somewhere in the neigh- 

 bourhood rocks of a highly siliceous character were erupted at a 

 period not later than the Lower Jurassic ; and when they are 

 found in position, it is possible that they may furnish proof of 

 the age of the granites which in many places pierce our Maitai 

 rocks, which are probably of Carboniferous age. 



Spherulitic felstone. — This is a compact light-grey felstone, 

 with abundance of spherulites about a quarter of an inch in 

 diameter. The spherulites have an opaque white centre, sur- 

 rounded by a broad dark brownish-grey ring, and show no outer 

 transparent zone. Occasionally, both the centre and the dark 

 ring may be seen with a lens to be composed of radiating fibres, 

 but this is not generally the case. The specific gravity of the 

 rock is 2-54. 



Under the microscope, with ordinary light, the rock is seen 

 to be a ground-mass without any crystals. With an inch objec- 

 tive this ground-mass shows as a colourless glass, hazy with 

 innumerable minute specs, which with a fifth objective often 

 show a greenish colour. With this power, also, the transparent 

 glass _ generally shows an indistinct granular appearance, but 

 occasionally there are irregular milky patches without any appear- 



* " Eeport of a Topographical and Geological Exploration of the 

 Western District of Nelson," by Julius Haast: Nelson, 1661, p. 109. 



