GEOLOGY. 
9G 
junction with the Buller the dip is towards the east, often as 
great as seventy-five degrees. They consist of regular beds of 
coarse loose sandstones, coloured by oxide of iron. On the eastern 
side of the Tiraumea plains, at the Buller, they consist of regular 
bands, from two to three feet broad, of greyish yellowish clay- 
marls, alternating with firm grained ferruginous sandstones, under 
which large pebble-beds appear. Sometimes the sandstones are 
micaceous, as at the junction of the Maruia with the Buller; often 
they are black from carbon, when found near shales, which in some 
places are common. Fossils are very rare, and with the exception 
of a few specimens of the genus dentalium, two specimens of 
pecten, identical with those found in the overlying limestones of 
the brown coal formation at Motupipi, I found only the remains 
of a bivalve shell, belonging to the freshwater mollusca, and being 
most nearly allied to Anodonta. 
Everywhere small seams of brown coal appear, of which the 
largest one, which I found in the Mangles, near its junction with 
the Buller, was three inches thick, but they all, without exception, 
appeared to thin out and to have been formed by driftwood, 
imbedded in spots fitted for its reception. In other places small 
patches of the same coal occur, as if formed by the carbonization 
of a single trunk. 
1 observed imbedded in sandstone, in the Buller, to the north of 
the junction of the Murchison, the trunk of a large tree com¬ 
pletely silicified, but still showing distinctly the annual rings. 
These seams of brown coal are accompanied by many very fine 
impressions of dicotyledonous leaves in the sandstones and shales, 
and in some places the leaves are still so well preserved that the'/ 
can be taken out of the rock in an almost perfect condition. 
All the above cited facts prove that these deposits have been 
accumulated in an estuary, marine and fresh water formations 
probably alternating, and indicate a frequent oscillation of the 
level during the period of deposition. The regular succession of 
gritty sandstones and soft argillaceous marls, alternating with per¬ 
fect regularity to a considerable altitude, proves further that these 
beds were deposited under re-occurring circumstances of similar 
character. It may have been that during heavy freshes in the rivers 
great quantities of sand and pebbles were brought down, and distri¬ 
buted upon the steep sides of hills lying beneath the waters of the 
estuary, and that when the freshes subsided, they only brought 
down mud and fine sand, which were spread over the underlying 
stratum; or it may have been that the direction of submarine 
currents was from time to time changed by the successive 
upheaval and depression of the shores. Whatever the cause, 
however, the alternation is very striking, and brings vividly before 
the mind of the explorer the fact that the same agencies which 
we observe daily in operation, worked without intermission during 
bygone ages, when the form of this island was entirely different. 
