144 
Allusion has already been made to the presence of restricted 
species in many of the sections. A distinction should be made in 
this respect between the molluscan beds and those containing 
mostly deeper sea forms, as it is from the former that such species 
have been principally recorded. The latter consist chiefly of 
limestones and polyzoal rocks, and the suddenness with which 
these occasionally replace the more littoral deposits has been 
frequently remarked upon. The relation of the two sets of strata 
is often puzzling, and they have, in fact, been arranged by 
separate authors in exactly reversed sequence. At Muddy Creek, 
as well as on the Glenelg and Murray Rivers, the shell beds 
merge rapidly into polyzoal rock, and their contemporaneous de- 
position is thus scarcely open to doubt. Close to Geelong the 
evidence is conflicting, since, though both classes of strata alter- 
nate, the limestone underlies at Belmont and in the Lower 
Moorabool, while higher up the same river, in the Maud section 
previously referred to, a thin littoral deposit rests upon one 
polyzoal rock, and is said to be overlain by another, with basalt 
intervening. At Spring Creek, however, which is 13 miles south 
of Geelong, our observations certainly indicate a contemporaneous 
origin for the two sets of strata. In this section the restricted 
forms are numerous, which fact alone seems to point to its com- 
parative isolation during the era of deposition, or, in other words, 
to its separation from the neighbouring land by tolerably deep 
water, the result being a colony or minor region of molluscan 
life, in which specialised forms might be expected to occur. 
It must not be forgotten that the great bulk of the Australian 
Eocenes consists of these polyzoal rocks and limestones, with 
their deeper sea fauna, and when in the midst of them, species 
peculiar to the laminarian or littoral zone suddenly appear, it is 
difficult to resist the conclusion that the latter were deposited on 
the shores of an island. When older rocks are elevated above the 
adjoining Tertiaries, as is the case at Geelong, on the south coast 
of Victoria, in the valley of the Glenelg, and elsewhere, we may 
safely decide that they represent either islands or peninsulas in 
the ancient seas, and the occasional presence of restricted species 
among the ordinary ones perhaps demands no further explanation. 
In the foregoing observations we have confined ourselves to 
broad outlines only. Many matters of detail, which naturally 
suggest themselves, cannot be discussed until our knowledge of 
the Tertiary areas is greatly increased. The questions raised, 
though deeply interesting, are confessedly difficult, and will 
perhaps not be finally settled for many years to come. 
