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PACIFIC SCIENCE, Vol. XXI, January 1967 
well-developed cleavage. The strike is 340° and 
the dip is nearly vertical. The banding in the 
argillite consists of tuffaceous sandstone, 3 mm 
thick, interbedded with argillaceous laminations 
0.5-1. 5 mm thick. In thin section, the green 
bands are seen to consist of sandstone with 
elongate grains of pyroxene, feldspar, and 
magnetite, set in a chloritic base. The red bands 
consist of argillite with a large proportion of 
hematite. Augen of hematite also occur in the 
sandstone bands. All the layers show graded 
bedding with laminations similar to those of the 
Greville formation. At the top of the forma- 
tion, spacing of bands is irregular and thicker 
than in the Greville formation, massive semi- 
banded silts (vuw 10663) becoming promi- 
nent. Tuffaceous, banded sediments near the 
top of the formation consist of oligoclase feld- 
spar, pyroxene, epidote, chlorite, and magnetite. 
All mineral grains show rounding. Green vol- 
canic tuffs (vuw 10662), massive or vesicular 
in hand specimens, appear near the top of the 
Waiua formation. The change in coloration 
from the uniform grey of the Greville forma- 
tion to the red and green of the Waiua forma- 
tion is attributed to a mixture of tuffaceous 
material. 
Stevens Formation 
The lower part of Stevens formation consists 
predominantly of massive, green, volcanic sand- 
stone and the upper part of tuffaceous siltstone. 
The contact between the upper and lower parts 
is abrupt and is probably a fault. The sandstone 
is 6,000 ft thick and dips vertically. The silt- 
stone is 5,000 ft thick and dips 60° E at 340°. 
The sandstone is hard, lacks cleavage planes, is 
resistant to erosion, and forms prominent hill 
crests. It consists of semirounded mineral grains 
0.03 mm in diameter, set in a chloritic matrix. 
Pyroxene and epidote are the chief components 
and the green color of the rock is due to altera- 
tion products of pyroxene. The siltstone is ex- 
posed in stream beds northeast of Tophouse 
Hotel. In thin section (vuw 10660), it appears 
to have an arkosic (oligoclase feldspar) com- 
position and a chloritic matrix. 
Alpine Greywacke 
Lower Mesozoic greywacke and argillite is 
exposed southeast of the Wairau Fault in the 
Tophouse district. No detailed study was made 
of these rocks, but the following points were 
noted: 
a. ) Greywacke southwest of Mt. Robert 
tends to be schistose and denser than 2.67 
gm/cc. 
b. ) The rocks of Mt. Robert and the St. 
Arnaud Range consist of 40% sandstone and 
60% argillite. The argillite is dark blue in 
color, shows well-developed cleavage, and is 
calcareous with prominent calcite veins. 
c. ) The rocks of the Raglan Range consist 
of 10-20% argillite and 80-90% sandstone. 
The sandstone is light-colored and hard, and 
consists predominantly of rounded quartz grains. 
d. ) Intraformational calcitic and hematized 
spilites (vuw 10685) are interbedded in the 
greywacke of the Raglan Range and the St. 
Arnaud Range. 
Quaternary Deposits 
Most of the Quarternary alluvial deposits in 
the Tophouse district represent glacial advance 
during the Pleistocene glaciation. 
The Tophouse gravels were deposited dur- 
ing the first recognized advance. The glaciers 
flowed from the site now occupied by Lake 
Rotoiti and, overriding the Brook Street vol- 
canics, flowed north along the Motupiko Val- 
ley. A branch glacier probably flowed west | 
over the Tophouse saddle and descended 2-5 
miles down the Wairau Valley (Henderson, 
1931:156). The lower limits of the glaciers 
were at 1,500-1,800 ft above the present sea 
level. 
The Wairau Fault 
The Wairau Fault is the major tectonic fea- 
ture in the Tophouse district and is probably 
an eastward extension of the Alpine Fault !; 
(Fig. 1). The fault was examined in the field, l 
but most of the information was obtained from I 
air photographs and is shown in Table 3 (with 
nomenclature adapted from Wellman, 1953) 
and plotted on the geological map (Fig. 2). 
The fault strikes eastward from Lake Rotoiti. 
Minor branch faults occur near Lake Rotoiti 
and along the northwest side of the Wairau 
Valley. Displaced and fault-aligned streams ; 
mark the fault trace on the north slopes of the 
St. Arnaud Range. The dip of the Wairau 
