Ultramafic Mass in New Zealand — Malahqff 
143 
TABLE 5 (continued) 
DENSITY 
ROCK 
MAGNETIC 
SUSCEPT., 
CGS UNIT 
DRY 
WET 
PART. 
* 
TYPE 
FORMATION 
X10-6 
2.44 
2.51 
2.62 
7 
greywacke sandstone 
Alpine facies 
2.61 
2.63 
2.66 
2 
greywacke sandstone 
(Raglan series) ? 
Alpine facies 
34 
2.67 
2.69 
2.72 
2 
haematitic chert 
(Raglan series) ? 
Alpine facies 
2.67 
2.68 
2.69 
1 
greywacke sandstone 
(Raglan series) ? 
Alpine facies ** 
39 
2.66 
2.67 
2.67 
1 
greywacke sandstone 
Alpine facies ** 
30 
2.63 
2.65 
2.67 
2 
greywacke sandstone 
Alpine facies ** 
120 
2.74 
2.75 
2.76 
1 
argillite 
Alpine facies ** 
74 
2.75 
2.76 
2.79 
1 
argillite 
Alpine facies ** 
2.74 
2.75 
2.77 
1 
argillite 
Alpine facies ** 
2.72 
2.72 
2.73 
0 
argillite 
Alpine facies ** 
2.66 
2.68 
2.70 
2 
greywacke conglomerate 
Alpine facies ** 
40 
2.67 
2.68 
2.69 
1 
greywacke sandstone 
Alpine facies 
49 
2.64 
2.65 
2.67 
1 
greywacke sandstone 
Alpine facies 
28 
2.82 
2.85 
2.90 
3 
calcareous spilite 
Alpine facies 
360 
* Porosity (%). 
* * Alpine facies 
(Mt. Robert 
series) . 
TABLE 6 
Preferred Densities of Rocks Used in Gravity Reductions of the Tophouse District 
DENSITY CONTRAST 
DENSITY 
WITH STANDARD 
rock 
(gm/cc) 
ROCK (GM/CC) 
Alpine greywacke 
2.70 
0.00 
Pleistocene gravels 
2.25 
—0.45 
Stevens form, siltstone 
2.78 
0.08 
Stevens form, sandstone 
2.92 
0.22 
Waiua form, banded slate 
2.82 
0.12 
Greville form, argillite 
2.74 
0.04 
Rangitoto form, limestone 
2.70 
0.00 
Te Anau ser. dolerite 
2.95 
0.25 
Te Anau ser. spilite 
2.90 
0.20 
Te Anau ser. red and 
green volcanic breccia 
2.95 
0.25 
Serpentinite 
2.65 
— 0.05 
Dunite, pyroxenite 
3.30 
0.50 
Brook Street volcanics 
(spilite) 
2.94 
0.24 
ity anomalies show up more clearly in the re- 
sidual gravity map (Fig. 4) and are quantita- 
tively related to the surface geology. 
The axis of the Brook Street high extends 
1 mile west of Tophouse and gravity values 
decrease in that direction. Anomaly contours 
below the value of + 16 mgal appear to extend 
in a southwest direction from Lake Rotoiti. The 
axis of the Brook Street high has a north-to- 
south trend above Tophouse. This direction is 
parallel to the strike of the Brook Street vol- 
canics, the Maitai series, and the strike of the 
Waimea Fault. The maximum positive value 
of 22 mgal is considered to indicate the position 
