184 Proceedings of the Royal Physical Soctety. 
they occur—their calcareous shells being very favourable for 
their preservation. sc 
Other animal remains have also been used as tests for the 
age of rocks, but till comparatively recently, in Britain, fossil 
plants have been entirely neglected for this purpose. On the 
Continent, however, much has been done by the aid of fossil 
plants in correlating and dividing the Carboniferous rocks into 
zones. 
The use of fossii plants for such purposes is fully justified 
in the admirable works of Geinitz, Weiss, Zeiller, Grand’ 
Eury, Renault, and others. 
At present I shall restrict my remarks to the correlation 
of the British Carboniferous rocks among themselves, and 
omit any reference to their foreign representatives, as the 
time at my disposal will not admit of my entering upon such 
a wide subject. 
In many of our Formations fossil plants are comparatively 
rare, and in such cases the Mollusca or other animal remains 
must serve as tests for the correlation of such rocks; but 
where plants occur in sufficient quantity, I believe that in 
all cases they give the surest index of age. 
I am aware that this is not the view generally taken, 
chiefly, I believe, because fossil plants have not been studied 
to nearly the same extent that animal remains have been. 
In Britain few of our paleontologists have devoted them- 
selves to the study of the fossil flora; but those who have 
gone into the subject carefully, have, I believe, fully recognised 
the value of plants for correlating strata. I need only instance 
two British paleontologists whose work proves this state- 
ment—Mr Clement Reid and Mr J. Starkie Gardner. 
Sir Archibald Geikie expresses a different opinion from that 
which I have adopted. He says, in writing of the Carboni- 
ferous system: “Fossil plants do not serve so well for purposes 
of geological classification as animal fossils;”! and again, 
“ As the conditions for the preservation of organic remains 
exist more favourably under the sea than on land, relics of 
marine must be far more abundantly conserved than those of 
terrestrial organisms. This is true to-day, and has doubtless 
1 Text-Book of Geology, 2nd ed., p. 782. 
