RELATIONSHIPS OF THE AUSTRALIAN CAINOZOIC SYSTEM. 
Although Capt. Hutton mentioned certain groups of animals 
which, by reason of their comparatively deep sea habitat, furnish 
species of world-wide distribution, it appears highly probable 
that even these particular forms would be prone to considerable 
variation should they survive in an environment differing from that 
of the open ocean ; and this will account for the difficulty of 
discovering universally distributed species for comparative purposes. 
To aid in this matter of the comparison of facies of widely separated 
faunas other than recent, it may be suggested that generic types, 
no matter of what group of organisms, but which are limited to 
distinct horizons in the northern hemisphere, should also be regarded 
as of special value in the correlation of the Tertiary strata in the 
southern hemisphere. A comparison of selected faunal types, more 
or less indicative of distinct horizons elsewhere, will be made in 
drawing up a suggested stratigraphical correlation, and discussed in 
the notes following in the next section. 
In connexion with this subject, it is also necessary to draw 
attention to the recent work of Dr. A. E. Ortmann* as having an im- 
portant bearing on the present question. From a study of the 
mollusca he has brought forward strong evidence in favour of 
correlating the Patagonian Tertiary beds with at least one of our 
southern Australian series, as weli as with the Pareora formation 
of New Zealand, all of which he regards as Lower Miocene. 
With particular reference to the percentage method, Ortmann 
remarksf : — “ In very many cases the age of the Tertiary deposits 
is determined by the percentage of living species found in them. 
In my opinion this line of evidence is entirely inadmissible in our 
case, and I hardly need to say anything to support this view ; this 
method may be safely used in Europe, but in the southern hemi- 
sphere it is out of the question.” 
Dr. Ortmann further points out that, owing to the changes 
in the systematic views of the various authors of species, the number 
of the identifiable living forms fluctuates, and one or two doubtful 
ones obviously lower the percentage considerably. This difficulty, 
as I have already mentioned, has frequently arisen in respect to the 
work of our Australian geologists, causing the same stratum to be 
referred to under three different age-names by as many authors. 
As a case in point, the work on the faunas of the Lower Muddy 
Creek section and the Spring Creek beds by Drs. Hall and Pritchard! 
showed a percentage of living species as low as 2.5 per cent, for 
the former locality, and only about 1 per cent, for the latter. Since 
only 3 out of 293 species were identifiable with living forms in 
the Spring Creek fauna, it is clear that by addition of a few more 
recent species these beds might be reversed in apparent sequence, 
by the opinion of the investigator of doubtfully valid living species. 
* Tom. supra cit. 
t Tom. cit., p. 288. 
J Proc. Roy. Soc. Viet., vol. viii., 1895, p. 190. 
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