422 Transactions. 



HYPEESTHENE-ANDESITE, 



South-east Flank op Mount Hikurangi, Whangarei District. 



A greyish porphyritic rock with idiomorphic phenocrysts of hypersthene, 

 coarse plagioclase from the acid end of the series, and rare brownish-green 

 hornblende. There are in addition numerous smaller lath-like feldspars, 

 arranged with noticeable parallelism, and some fairly large sporadic iron- 

 ore crystals, enclosed with the major phenocrysts in a somewhat lithoidal 

 irresolvable matrix in which magnetite specks furnish the only recognizable 

 mineral, and which appears to be densely cryptocrystalline. The hyper- 

 sthene is not plentiful, and is only in small crystals in the two sections cut, 

 though occasional crystals reaching as much as 1 J in. in length can be 

 gathered in the field. 



Art. XXXV. — The Conglomerate at Albany, Lucas Creek, Waitemata 



Harbour. 



By J. A. Bartrum, Auckland University College. 



[Read before the Auckland Institute, 22nd December, 1919 ; received by Editor, 31st 



^ December, 1919 ; issued separately, 16th July, 1920.} 



I 



Plate XXIX. 



About 200 yards up-stream from the lower wharf at Albany (see locality 

 map), conglomerate bands outcrop which have given rise to abundant cobbles 

 strewing the banks of Lucas Creek in the vicinity. They are without 

 doubt members of the local Tertiary sequence known as the Waitemata 

 beds, but their horizon therein is doubtful, for folding and faulting are 

 common in the sandstones on the shores of the upper Waitemata Harbour 

 (into which Lucas Creek flows) and obscure the sequence. The writer is 

 inclined to place the conglomerate bands amongst the lowest of the Waite- 

 mata beds in the near vicinity of Auckland, but there is at present no 

 means of fixing their absolute horizon, and, as the purpose of this paper 

 lies rather in the direction of describing the interesting assortment of rock- 

 varieties in the bands than in discussing their stratigraphy, this aspect will 

 not receive further attention herein. 



The main band of conglomerate near Albany is about 12 ft. thick, and 

 has a strike that is approximately north-east by east and south-west by 

 west, and a dip of 45° up-stream to the north-west by north. About 20 ft. 

 beneath it is a similar band of smaller cobbles 2 ft. in thickness. Not many 

 yards down-stream the direction of dip is reversed, the sandstones dipping 

 gently in an approximately south-east direction. The actual reason for the 

 reversal is obscure : it may be anticlinal structure, for there is evidence at 

 Riverhead favouring this explanation, although the conglomerate was not 

 found to reoccur in the down-stream section.* 



* A much-weathered coarse conglomerate is exposed at Cut Hill, about two miles 

 south-south-east of the Albany outcrop, but it appears that this band is not the same 

 as the Albany one. 



