424 Transactions. 



The material of the bands consists of very-well-rounded pebbles and 

 boulders usually a few inches in diameter, but reaching as much as \\ ft., 

 set in fine mortar ; they appear typical sea-beach drift, a conclusion borne 

 out by the discovery of shell-fragments in a somewhat calcareous fine grit- 

 conglomerate about 20 ft. to 25 ft. in depth overlying the upper conglome- 

 rate band, and outcropping, therefore, up-stream from it. In facies these 

 boulders consist mainly (perhaps 90 ^ per cent.) of rocks of holocrystalline 

 igneous character, many distinctly gneissic in structure, along with grey- 

 wackes, andesites, and occasional trachytes and cherts. 



No attempt was made to trace these conglomerate bands across the 

 low hills, rising to about 400 ft. above sea-level, immediately west of 

 Lucas Creek, because of the heaw overburden of residual clav general 

 upon the hills of the district ; they were looked for and picked up 

 again in the low-lying wide basin adjoining the Rangitopuni and Mahoenu 

 Streams (see locality map), into which the roads from Albany to Riverhead 

 descend, and where one can find not only distinctive shoading but also 

 several outcrops adjacent to the main road to Riverhead. About two 

 miles east of this latter place, just above the conglomerate is a quartz-rich 

 grit which passes into a fine grit-breccia about 1 ft. in depth, containing 

 fragments of wood, pumice, and a very dense felsitic mica-rhyolite in 

 fragments ranging up to |in. in diameter The dip is about 80° to the 

 south-south-west. In the main conglomerate band of this outcrop jasperoid 

 argillite, greywacke, and a good deal of andesite, some of it very coarsely 

 porphyritic and very strongly oxidized, are frequent, in addition to the 

 dioritic types common at Albany. Towards Riverhead the band of grit- 

 breccia characterized by the pumice and other rhyolite thickens consider- 

 ably, and the material also is coarser, forming a very curious firmly 

 cemented breccia where it is exposed in the tideway near the paper-mills 

 at Riverhead. It is not far above the main conglomerate band — here of 

 much smaller pebbles than elsewhere ; below this latter also are several 

 distinct bands, each about 2 ft. in depth, of fairly coarse conglomerate. 

 The tide was unsuitable for close investigation of these bands during the 

 writer's visit, but they did not appear to be of special interest. 



Petrography op the Conglomerate Bands. 



In a recent volume of these Transactions the writer (Bartrum, 1917) 

 described gneissic diorites discovered in loose boulders at Albany, and 

 suggested that they had come from a boulder-bed known to outcrop 

 near by in the Waitemata beds. Upon visiting the locality he soon found 

 that his surmise was correct, and recognized several other rock-types in 

 addition to the two represented in the specimens first given to him. There 

 are several plutonic types, which nearly all show the effects of considerable 

 pressure' notably granulation in various stages of intensity. The complete 

 list is as follows : — 



(a.) Rocks of sedimentary facies. 



1. Greywackes (fairly common). 



2. Jasperoid argillite (rare). 



3. Chert (rare). 



No particular attention was accorded the pebbles of sedimentary facies, 

 as the writer's interest lay chiefly with the igneous types, so that the above 

 list may be very incomplete. The greywackes and argillite are obviously 

 derived from the " Maitai " rocks, which form the basement of the 

 Waitemata beds. The chert resembles rocks of similar appearance which 



