102 
GEOLOGY. 
stream, on descending tlie Grey, I found the sandstone ceased, 
and a magnificent porphyritic granite appeared, intruding its 
masses into that rock, affecting however but little the strike and 
dip previously observed. The granite itself becomes, where it 
penetrates the flaggy sandstone beds in tortuous veins, charged 
with mica, the large feldspar crystals disappearing. The sandstone 
beds close to the contact are altered to mica schists. Tifty yards 
from the line of contact I met them again, having succeeded in 
climbing down to the river’s edge in order to obtain a view of the 
section. The sandstones there had a semi-crystalline appearance, 
the same strike and dip ; the mica had disappeared from the body 
of the rock itself, but in the numerous joints which intersected 
the strata, a great quantity of mica scales were to be found, 
showing in a very instructive manner, that the altering powers of 
the granitic veins were not strong enough here to effect the same 
changes as they did near the immediate contact, but that they 
were still in sufficient vigour, where unopposed by the resistance 
of the compact rock, to form mica scales. Two miles lower down the 
Grey we meet with large masses of granulite, with garnet crystals, 
striking always in the same direction. The granite shows itself 
also in the Grey plains, forming here and there, in the river bed, 
low cliffs, often in contact ' with sedimentary rocks, which are 
invariably altered into granulites or micaceous schists. The 
formation of the Grey plains is of a very interesting nature, 
showing what great changes have occurred in the level of this 
island in (geologically speaking) recent times. In the northern¬ 
most part of these plains low cretaceous hills occur, which slope 
down to the northern bank of the Buller. From the Buller the 
whole of the plains as far south as Lake Brunner are covered with 
drift formation and old alluvium, the only place where cretaceous 
rocks, a limestone charged with mica, crop out, being in the 
Inangahua, at its confluence with the Buller, and for eight miles 
up the former river. More towards the south, in the Grey, the 
bed of which I examined closely, these older strata cease, and a 
younger tertiary formation (pliocene?) directly overlies the granite. 
It consists of a coarse pebble bed, cemented by an argillaceous 
matrix, on which reposes a stratified bluish or greyish clay, full of 
silvery mica scales, alternating with small seams of lignite, also 
full of mica, and with beds of sand. These strata reach, on the 
eastern side of the plains, an altitude of one hundred feet, and 
are there overlaid by great quantities of till. 
I obtained here the following sections, taken in ascending 
order:— ° 
12 feet pebble bed. 
3 feet greenish clays, with scales of mica, and pieces of drift-wood changed 
into lignite. 
2 feet sands, composed of grains of quartz and scales of mica. 
ieet bluish clay marls, changing in their uppermost part into slate clays. 
