117 
that at Spring Creek would jump up or down, as the case might 
be, a half per cent. at once. Indeed, for one or two of the 
Muddy Creek species referred to, their identification with living 
forms is not absolutely positive, so that too much stress must not 
be laid on even this low percentage. Messrs. Hall & Pritchard’s 
calculations for Spring Creek are based upon a total of 293 
species of mollusca from the beds. Our list, corrected by supply- 
ing a few omissions, and adding the remainder of the Pleuro- 
tomide, gives 275 species, which is a fairly close agreement. 
A. sufficient number of species has now been elaborated from 
Muddy Creek and Spring Creek to allow of a comparison between 
them on a somewhat different basis, which may prove useful with 
such closely allied beds. The Miocene deposit resting upon the 
Eocene at Muddy Creek has, up to the present, yielded 244 
species of mollusca, and that at Jemmy’s Point about half this 
number. Now, it is curious to note that of the 275 species on 
our list for Spring Creek, 16, or 5°8 per cent., pass up into the 
Miocene, while out of the 649 species in the Muddy Creek 
Eocene, 30 species pass up, or only 4:6 per cent., which is un- 
favorable to the inferior horizon claimed for Spring Creek. In 
fact, the presence of such characteristic Miocene forms at Spring 
Creek as Mactra axiniformis, Ancillaria orycta, Dosinia John- 
stoni, &c., is a distinct factor in the general facies of the fauna, 
and must be taken into account in estimating its age. 
According to the summary at the end of their paper, Messrs. 
Hall & Pritchard make the Eocene sands of Muddy Creek rest 
upon the polyzoal rock, and this again upon the Older Volcanic. 
The Older Volcanic is wanting in South-Western Victoria, at 
least in the neighbourhood of the Tertiaries, the basal rocks, 
where visible, being either Mesozoic strata or a still more ancient 
porphyry, but the polyzoal limestone attains a much greater 
development there than in the Geelong District. Moreover, that 
this rock really underlies the Eocene sands may well be doubted ; 
more probably it is coterminous with them. On the Grange 
Burn itis found ata low level certainly, but a section, seen at 
our last visit near the Falls in Muddy Creek itself, showed an 
apparent gradual passage from gastropod beds into typical poly- 
zoal rock. ‘The same is the case at Spring Creek, and presumably 
also at the North Belmont section, judging frem its description 
in Messrs. Hall & Pritchard’s paper.* Possibly, some sections in 
the Geelong District may show the rock in an inferior position, 
but this does not appear to be universal, especially in the 
Western District, where the formation is best studied. 
It is notable that in almost every exposure of Eocene strata, 
*Compare pages 191 and 194, Older Tertiaries of Maude. 
