Bartrum. — The Conglomerate at Albany. 425 



are common in the liydraulic limestone member of the Oamaru system 

 of Marshall (1911, pp. 22 et seq.) ; such an origin would raise no fresh 

 difficulty, for Hector (Cox, 1881, p. 29) and Henderson (1914, p. 157) have 

 observed pebbles of the hydraulic limestone itself in Tertiary conglomerates 

 in various places in the Warkworth-Mahurangi district and elsewhere, 

 from which Henderson has deduced the discontinuity of sequenc^e of the 

 rocks of the Oamaru system in that district, which is not far distant from 

 Albany. ' 



(b.) Rocks of igneous origin. 



1. Granodiorite (granulated). 



2. Quartz-diorite (granulated). 

 .3. Banded dioritic gneiss. 



4. Diorite (granulated)". 



5. Anorthosite. 



6. Dolerites. 



7. Andesites of varied type. 



8. Trachytes. 



9. Rhyolite (not in the main boulder-band itself). 



The granulated ^iorites preponderate amongst the igneous types, and 

 must constitute 80 per cent, of the pebbles in the outcrop of the con- 

 glomerate at Albany. 



Description of Types. 



1. Granodiorite (granulated). 

 A fairly common type. A fresh coarse-grained rock, outwardly dioritic 

 and rich in hornblende. In section notably and coarsely ophitic (see 

 Plate XXIX, fig. 1). The light-coloured minerals comprise nearly two-thirds 

 of the rock : basic andesine is the most abundant of them, and next in 

 order come orthoclase and quartz, this last interstitial and abundant. 

 The darker minerals consist of a very little coarse iron-ore and large 

 hornblende crystals enclosing smaller ones of andesine in perfect ophitic 

 manner. A little apatite furnishes the only accessory besides the iron- 

 ore. The efiects of severe pressure are very obvious — shadow extinction 

 and 'granulation of quartz and sometimes orthoclase, and bending of the 

 twinning lamellae of the plagioclase. 



2. Quartz-diorite (granulated). 



This type was described in an earlier paper by the writer (Bartrum, 

 1917, p. 423) ; it approaches the granodiorite mineralogically, but differs 

 from it structurally. 



3. Bamled Dioritic Gneiss. 



The banded structure is quite obvious in hand-specimen. In section 

 it is somewhat lost sight of owing to the mosaic-like structure resulting 

 from complete granulation (see Plate XXIX, fig. 2). In composition it is 

 practically the same as the general granulated diorite next to be described, 

 and there is no need to supplement the brief description of this type 

 published in the earlier paper just referred to. 



4. Diorite (granulated). 



Judging by macroscopic examination, the vast majority of the pebbles 



and boulders of the conglomerate belong to this type — a moderately fine 



even-grained dioritic rock, showing numerous glistening feldspars and darker 



amphiboles. Usually under the microscope there is sufficient granulation 



