166 WISE 
The black ironsands apparently derive from the Taranaki andesites of Mt 
Egmont (Williams 1974: 135) and have been drifted northwards by coastal sea 
currents as far as Muriwai Beach west of Auckland (Schofield 1970, Williams 1974). 
Nicholson & Fyfe (1958) recorded the magnetically separable ironsand concentrations 
along that coast. While there are variations in the percentages at various localities 
there is a distinct drop along Muriwai Beach from 10% 3.2 km (2 miles) north of 
Muriwai to 2% at 4.8 km (3 miles) and less than 1% 6.4-48.2 km (4-30 miles) north. 
J.C. Schofield, in his paper on coastal sands of Northland and Auckland 
(Schofield 1970), presented data for the coastal areas under consideration in the 
present study. In general, coastal sands from Waikato River area have high mafic 
content (which includes black ironsands), low quartz and medium residue (mainly 
rock fragments) percentages (ibid. Table 1). On Muriwai Beach there are high mafics, 
low quartz and low residues at the south end; medium values for mafics and quartz, 
low for residues towards the north (ibid. Table 3, Fig. 6). Further north to Hokianga 
and North Cape (ibid. Tables 4,5) there are some increases in quartz with mafics and 
residues remaining low, including a further quartz increase at Spirits Bay on the 
extreme north coast (ibid. Table 5). South of Parengarenga Hbr. on the far northern 
east coast the quartz percentages are very high (over 90%) and only a little less 
southwards to Karikari Pen., with almost no mafics or residues (ibid. Table 5, p.795). 
There is a major change east of Karikari Pen., the north-east coast is typified by low- 
medium quartz, low mafics and medium-high residue content (rock debris) which 
accounts for the pinkish-brown colour of the sands (ibid. Table 6, p.798). From the 
Whangarei Hbr. area south to Pakiri there is another major change with the 
occurrence of greyish white sands. Percentages of quartz are low-medium, mafics and 
residues are low but soda-calc feldspars, which elsewhere are mostly low (occasionally 
low-medium), are here high being over 60% (ibid. Table 7, p.804). 
The sands of the northern coast-line thus show both gradual changes and distinct 
compositional differences in areas of interest in this study. 
COASTAL TIGER BEETLES 
Local and seasonal activity 
Coastal tiger beetles occur on sand-dunes behind ocean beaches on northern 
North I coasts. In the summer season they are typically active on the front of fore- 
dunes and forage at the top of beaches. However, they are often more common beside 
beach entrances and stream banks where streams debouch through the dunes. 
Presumably these breaks in the dunes allow off-shore breezes, even if light airs, to 
carry a food supply of small insects to the dune banks and the streams supply flying 
aquatic insects. Tiger beetle colonies are able to tolerate human activity even on 
frequently used beaches where active beetles are sometimes seen between groups of 
picnickers. Permanent habitation along beaches may, however, affect colonies. 
