256 PROCEEDINGS OF SECTION C. 



The following pai'tial analyses, made by Mr. W. Skey in 1869, 

 have been published. 



I. — A little altered rock in Freeman's Bay Claim, Warotahi Creek. 

 II.— A more altei'ed rock from the first dyke-like mass up Tararu Creek. 

 III. — A still more altered rock from the dyke-like mass below the old 

 Point, Russell claim, Moanataiari Creek. 



The ground-mass is generally small in quantity, colourless, and 

 more or less devitrified, but in the specimen from the deep levels 

 of the Imperial Crown Mine it is faii'ly abundant, and composed 

 of a pale brown glass. In another specimen fi'om the Waiotahi 

 it is also an abundant brown glass crowded with felspar microlites 

 which show no signs of iiuxion structure. Many of them have 

 chloritic infiltrations. 



The felspars in the less altered rocks are clear and zoned with 

 inclusions. They generally shew twinning on the albite type, but 

 in the Tararu rock twinning on the pericline type occurs also. 



Binary twins are not infrequent, but all are I believe plagio- 

 clase. Two different individuals gave extinction angles on either 

 side of the composition face of 20° and 18° = 38°, and of 15° and 

 13° = 28°. Neither of these binary twins could therefore be 

 monoclinic, but they may be oligoclase. In the more altered 

 rocks the felspars get cloudy, generally in the centre, but some- 

 times along cracks and round the margin, until they are entirely 

 decomposed ; and this lends support to the idea that these are 

 two difterent kinds of plagioclase in the rock. In two specimens 

 they are infiltrated with chlorite ; in one of these the infiltrated 

 felspars are clear, in the other they are decomposed. 



Augite.^ — Pale green or yellowish-brown, not pleochroic, in square 

 or rectangular prisms, the prismatic faces scarcely developed, and 

 the orthopinacoids sometimes rather longer than the clinopina- 

 coids. They often shew polysynthetic twinning along a central 

 band. Prismatic cleavage is not always well developed ; in one 

 case a clinopinacoidal cleavage is more apparent, crossing the 

 twinning plate at right angles. Polarization colours brilliant. 

 Angle c : ^ = 39°. Inclusions minute or none. 



