GEOLOGY AND MINERALOGY. 
69 
according to their nature ; often the harder rock, lying side by side 
with those of different quality, is left standing while its adjacent 
ground disappears. We have already noticed this in the case of 
the large dike traversing the Sandy Bay crater, and to which we 
shall again recur in connexion with the subject now before us. 
There are, however, in addition to that dike, other large ones inter- 
secting the edge of the crater, whicli by the same process have been 
laid bare ; some of these are of considerable size, and, although not 
so conspicuous and easily traced as the Great Lot dike, they all 
partake of the same general direction and lie parallel with it. At 
intervals, where the directions coincide, the crater edge itself is at 
present formed for some distance by the exposed edge of a dike. 
This may be seen to the westward of Diana’s Peak, where 
the narrow roadway leading to the highest mountain top appears 
to pass along the top of a wall, this wall being nothing more 
than the dike itself, with perpendicular faces of a hundred feet 
or more, and a width of only eight or ten feet. But for the ferns 
nnd other native vegetation which thickly clothe it, and conceal the 
danger, this perilous way would certainly be less popular with 
pleasure-seekers and pic-nic parties en route for Diana’s Peak. The 
edge of the crater, about three miles further to the westward, a little 
beyond West Lodge, is again cut by some of these dikes crossing it 
at very acute angles. Three of them of considerable thickness, but 
not rendered so strikingly conspicuous by denudation of the sur- 
rounding rocks, lie within the space of half a mile ; and, although 
placed in such near proximity to one another, differ entirely in 
composition. Proceeding in the direction already indicated, to a 
short distance beyond the old Piquet House on the ridge, we arrive 
at the first of these dikes. It is composed of a compact dolerite, of 
a deep brownish hue, containing disseminated augite and chrysolite. 
Partly amygdaloidal and zeolitic, the cavities being filled or lined 
^ith minute white transparent crystals in form resembling chabazite. 
Massive boulders of this rock have become detached and rolled down 
the hillside, where they lie scattered about, protruding above 
the grassy slopes on either side of the road leading from West 
Lodge down to Thompson’s Wood. Upon nearing Thompson’s Wood 
House, where a small patch of weather-beaten Pine trees stands in its 
*ear, other boulders similarly lodged occur, but of a somewhat more 
laminated character. Their composition also is found on exami- 
