COLONIAL GEOLOGY. 
177 
arcli that might hare been built by gigantic Titans ; a little further, and 
there is a basaltic stack rivalling a cathedral in dimensions, or a lofty 
pillar, poised on a slender base, rears itself in some sheltered bay. 
Xear Western-Port entrance, the basalt dips downwards into a sort of 
basin, in which a whitish Tertiary rock, looking at a distance like chalk, but 
very different in appearance from that rock when closely examined, has 
been deposited, and is literally built up of spines of Echinidae, shells of 
inollusca, and the broken carapaces of large crustaceans. The whole of 
these remains, with the exception of the spines, are much broken ; the 
latter are so well preserved that youths in the neighbourhood collect them 
to u;?e as slate-pencils : for such a purpose they answer most admirably. 
About a mile westerly from this rock, the upper portion of the basalt 
having been denuded down to the water's edge, a pavement of hexagonal 
and pentagonal blocks is displayed. These, the blocks, are of such regu- 
larity as to resemble a work of art rather than one of nature. Here, as in 
most portions of the district along the coast, the basalt is arranged in a 
manner which resembles stratification. First of all, at the sea-level, or 
near it, is a compact rock, sometimes columnar, although from its low level 
this feature is not particularly noticeable, unless, as in the case above cited, 
the ends of the columns are laid bare ; next there is a thin bed of red- 
ochrish clay, comparatively soft and friable ; and above, forming the 
summit of the clifls, save where tlie limestone appears as a capping, is a 
thick mass of basalt, only rudel}-, if at all of a columnar structure. 
No idea can be formed of the extent downwards of this lower bed, it 
never having been passed through. The thickness must, however, be con- 
siderable, since basalt only assumes a crystalline form when collected and 
cooled in large masses. 
As a rough guess, I would suggest that the entire formation is the result 
of at least two outbursts of molten material, and that the clayey stratum 
referred to had collected either as scum and scoriae arising from tlie molten 
matter, or as detritus deposited thereon by aqueous agency. Over this the 
upper basalt was afterwards poured out. Subsequently the district sunk 
beneath the sea, allowing Tertiary rocks, after covering the whole, to be 
deposited ; last of all, the formation was raised to its present level, and the 
process of denudation commenced. 
This denudation would be greatly facilitated by the existence of the soft 
layer just referred to. On this the waves, as they do at present in eating 
out caves and arches, would act successfully. Once undermined to any 
great extent, the fall of large portions of cliff would be a matter of cer- 
tainty, and strewn upon the beach as boulders and shingle kept in motion 
by successive surges, every fragment would act the part of a muller grind- 
ing and being ground to powder ; thus the talus would be cleared away, 
and the sea would be permitted once more to eat away the soft and yield- 
ing stratum. 
lieflecting upon these phenomena, the mind is naturally astonished at 
the idea of a sea of molten materials stretching over an area of fully two 
hundred square miles. Nor is the subsequent wasting away and denuda- 
tion by waves and ocean currents, to the extent which becomes evident by 
a merely casual observation, one whit less startling. Basalt similar in 
mineralogical character, and of like geologic age, forms the surface-rock of 
Philip, is covered by a thin capping of Tertiary deposits in French Island, 
and overlies the Carboniferous strata on the adjoining mainland near 
Griffith Point. No one examining these several basaltic masses can 
doubt of their having been once continuous. The various channels lead- 
TOL. VII. 2 A. - ^ 
