GEOLOGY. 
93 
ti’om the application, for a short time only, of the greatest hitherto 
experienced abyssological powers. 
dhe action ot the waters is still more visible on Mount Robert, 
where.they have worked three large and deep valleys, running 
eastw ard from the central ridge towards the southern extremity 
°u-.+ j Roto-iti lake. The valleys are broadest in the middle 
altitude ot the mountain, and narrow, before they reach the lake, 
o mere gorges. The main ridge itself, sloping abruptly towards 
the w est, is olten so sharp as to leave merely space for one’s foot- 
i mc ’. untain many places is only covered with forest to 
an altitude ot 3,000 teet, above which a barren desert begins, 
strew ed with angular pieces of rock of all dimensions. As the 
agencies which have produced these effects are still carrying on 
tiieii perpetual work of destruction, it is clear that no vegetation 
capable of giving firmness to the rubbish can spring up. The 
wdiole scenery presents, in fact, an image of utter desolation and 
waste, and it is only here and there, where comparatively level 
spots occur upon the ridge, and upon its more moderate de¬ 
clivities, that we find an Alpine vegetation, forming occasionally 
a lovely carpet of flowers, springing from the desolation around, 
and contrasting agreeably with the bizarre forms of the rocky 
points about it. 
Here, again, we observe that the two mighty agencies which 
determine the form of the surface of our globe endeavour to coun¬ 
teract each other, for whilst the abyssological force upheaves or 
depresses, the atmospheric destroys and levels, both continuing 
their slow but incessant work for myriads upon myriads of years. 
The granite near Lake Rotoroa diminishes in extent towards the 
south, and a change into gneiss-granite and granulites, containing 
a great quantity of garnets, is traceable, between which amphibo¬ 
lites predominate. In the upper Mangles a vein of almost pure 
magnetic iron ore appears, which, with a strike nearly north and 
south, and a dip of 79 degrees towards the east, intersects the 
granite, and has a breadth of twelve to fourteen feet. At the 
southern side of the Roto-roa we meet with an assemblage of 
eruptive rocks, which have broken through the amphibolite, and 
which appear most conspicuously in the magnificent dome-shaped 
Mount Hutton, at the southern corner of the lake, composed of a 
beautiful red augitic porphyry. 
More towards the west two other mountains of almost equal 
size appear, formed of diallage and hypersthene rocks, the nearest 
of which to Mount Hutton I called Mount Playfair, placing the 
name of the pupil and friend in conjunction with that of his and 
our great instructor. More towards the south, on the eastern, 
side of the Spencer mountains, we find a whole series of diabasic 
rocks, diabases, aphanites, llerzolithes, porphyries, and amygda- 
loids, occasionally rising in magnificent cones over the surround¬ 
ing country, of which Mount Smith, lying at the foot of Mount 
