GEOLOGY. 
101 
brought down by adjacent streams, and indicating, by a difference 
in the size ol the particles in the various layers, whether the 
stream by which they were deposited was at the time swollen or 
i ^ other points, close to the mountain gorges, they exhibit 
lie character ot the delta ot a torrent, consisting almost exclusively 
o boulders, which from year to year narrowed by their accumu- 
a ion that part ot the lake, whilst in its central part we meet with 
reshwater marls ot a bluish colour. Here, as at Lake Roto-roa, 
1 observed also that at the northern end, where the waters had to 
hnd their outlet, hornblende rocks strike across the valley, which, 
from their hardness, ottered greater resistance to the action of 
water than the adjoining granitic rocks, which were more easily 
decomposed. J 
My endeavours to find fossils in the slaty rocks of this chain were 
not crowned with success, but, from their lithological character, 
we may presume that as they resemble closely the rocks of the 
Cambrian and Silurian age in other parts of the world, they too 
have been formed in those remote periods. The boulders and 
angular pieces in the Grey, where it enters the opening, as well as 
those of the Maruia itself, south of Mount Mueller, show that this 
depression is the eastern boundary of the granite, which from this 
point strikes towards the south-south-west. It is without doubt, 
that the thermal springs discovered by Messrs. Lewis and Maling 
near the banks of the Maruia, in the Cannibals’ Gorge, take their 
rise at the line of contact of these rocks. I have laid down in the 
preceding pages what I was able to observe in these central 
ranges, and I must leave it to other geologists, when this now 
inhospitable country has been rendered more accessible, and 
therefore, when they will not labour under the same disadvantages 
that I did, to fill up the details of the geological map of this 
province, in which I could only lay down with accuracy that part 
of the country of which I obtained actual sections, although my 
successor will, I think, find ■ that the general geological features 
which I have filled up, partly by induction, and partly by judging 
from angular pieces of rock brought down by the torrents, will not 
be far from correct. 
On the western bank of the Alexander stream we meet, for the 
first time, with a sedimentary rock of newer origin than those of 
the central chain; an arenaceous sandstone of greenish yellow 
colour, with veins of quartz, striking north and south, with a dip 
of forty-five degrees towards the west. In a few places casts of 
small shells are visible, but not sufficiently distinct to enable me 
to form any conclusion respecting them. This sandstone overlies 
the gneiss granite encircling Black-hill, and reaches, in the 
Herschel mountains, a considerable altitude; forming, on the 
banks of the Grey, hills only a few hundred feet high, it has been 
altered in many places in the most interesting manner, of which I 
shall state p few instances. About a mile from the Alexander 
