118 REPORTS ON THE STATE OF SCIENCE.—1917. 
been regarded as much later than the lower part. But, according to 
Arber, the specimen on which T. Sweeti was founded is so imperfect 
that the genus is indeterminable. The Bacchus Marsh Sandstones 
with Gangamopteris are generally correlated with the Lower Coal 
Measures of New South Wales, through Kitson’s proof that the glacial 
beds on the northern coast of Tasmania are of that age. 
The correlation suggested for the beds of Eastern Australia may be 
tabulated as on next page. 
If this correlation be correct, the use of the term Permo-Carbont- 
ferous is one of definition and there are four available courses: 
(1) To retain Permo-Carboniferous for some undefined parts of both 
the Carboniferous and Permian. 
(2) To retain it for the combined Uralian-Artinskian as a passage 
series. 
(3) To abandon it by referring all the beds above the unconformity 
at the top of the Lepidodendron beds to the Permian—the course 
followed by Frech. 
(4) To abandon it by referring the beds above that unconformity 
and the top of the Upper Marine series (with the exception perhaps ol 
the Aneimites beds) to the Upper Carboniferous (Uralian), and by 
assigning all the beds above the Upper Marine series to the Permian 
(Punjaubian). 
Of these four courses the last seems to me the best, for the first 
doubles the difficulty of definition and retains a provisional term after 
it has served its purpose; according to the second, the term is unneces- 
sary; and the paleontological evidence is against the third. 
The correlation suggested is open to one objection, based on 
geo-tectonic grounds. According to it, the Middle Carboniferous in 
Australia was a great period of earth movement and non-deposition. 
In N.W. Europe the corresponding disturbances were in the Upper 
Carboniferous. If the earth movements in Europe and Australia were 
necessarily synchronous, then the Australian beds here assigned to the 
Uralian must be referred to the Moscovian. The paleontological 
evidence appears entitled to more weight than the geo-tectonic. 
While there is so much difference of opinion as to the system to 
which these beds belong, it may seem premature to attempt to determine 
their series. But the system can only be settled by agreeing which 
of the beds are Upper Carboniferous and which are Lower Permian. 
The problem appears easier in Australia than in South Africa, where 
there is continuous sequence from the Carboniferous to the Jurassic 
and there are no Marine beds to help the correlation. 
The main argument against attempting a definite correlation with 
the European horizons is based on the doctrine of homotaxis. That 
principle seemed so reasonable that it required careful consideration. 
According to the present trend of opinion, the importance once attached 
to homotaxis was exaggerated. Huxley raised the question whether the 
Carboniferous fauna in Kurope might have been contemporaneous with 
the Devonian fauna in Australia. That question has now been generally 
answered in the negative, since the geological time was so vast that 
the length required for the spread of a marine fauna from one sea 
