ON THE ROCKS OF THE IIAURAKI GOLD-FIELDS. 251 



Calcite occurs in the decomposed felspars and liornblendes in 

 the Tararu rock, but I could detect none in those from Waiotahi. 



Titaniferous-magnetite, in large grains, occurs sometimes 

 sparingly, sometimes abundantly, but there is A^ery little magnetite 

 dust in the ground-mass. In the Tararu specimen it is changed 

 into leucoxene. Secondary magnetite occurs in connection with 

 the chlorite, 



Pyi'ites is seen occasionally, sometimes associated with the 

 magnetite, but it is in small specks, and in the Tararu specimen is 

 changed into limonite. 



Enstatite Dacite. — T have a single specimen of this rock from 

 a boulder in Waiotahi Creek. It is compact, dark greenish-grey 

 in colour, and with greenish-white felspars. The specific gravity 

 is 2.703. Under the microscope the ground-mass is seen to be 

 abundant, composed of a clear glass, with brownish clouds of 

 globulites, and thickly dusted with magnetite. 



Felspars are clean, well-twinned plagioclase, strongly zoned with 

 inclusions and negative crystals. They average about 0.025 inch 

 in length. Binary twins also occur. 



Quartz (original) is rare, seldom more than one piece in a slide, 

 but when it occurs it is in rather large (0.027 inch) angular frag- 

 ments, with the same inclusions as the quartz described in the 

 hornblende dacites. 



Bastite, in irregular prisms, with a well-marked cleavage. 

 Interference figure sometimes visible, shewing the axial plane to 

 be at right angles to the cleavage. Pleochroism well marked, and 

 pale yellowish ; /3 and y bluish-green. It contains inclusions of 

 apatite. 



Chlorite, of a blue-green colour, is in some of the pyroxenes. 

 It is isotropic and not pleochroic. 



Calcite, as minute grains in the centre of some of the felspars. 



Magnetite, in large grains as well as disseminated through the 

 base. Also secondary with chlorite. 



There is no pyrites in this specimen, 



I am not aware of any enstatite dacite having been previously 

 described. 



Hornblende Andesite. — Of these I have five examples. One 

 from the first hard mass of rock, or dyke, up Karaka Creek ; 

 another from a boulder in Waiotahi Creek ; a third from the dyke 

 on the shore a little north of the mouth of Tapu Creek, and two 

 from Coramandel. One of these rocks — from Omaru Island, 

 Coromandel — differs max^kedly from the others, and I will describe 

 it separately later in the paper. The rest are compact greenish- 

 grey rocks, darker than the hornblende dacites, but lighter than 

 the augite andesites, and porphyritic minerals are not conspicuous 

 in any of them. The specific gravity ranges fi*om 2.G65 to 2.728. 



