186 Proceedings of the Royal Physical Society. 
consequently the less likely to be able to withstand the 
influences of changing climate and other physical conditions. 
A living species of Foraminifer or Brachiopod, endowed with 
comparative indifference to its environment, may spread over 
a vast area of the sea-floor; and the same want of sensibility 
enables it to endure through the changing physical conditions 
of successive geological periods. It may thus possess a great 
range both in space and time. But a highly specialised 
mammal is usually confined but to a limited extent of 
country, and to a narrow chronological range.” } 
This extract fully illustrates the views generally held by 
paleontologists, and the reasons why they hold them. But 
the very reasons on which they place so much importance 
on the Mollusca for the identification of strata are those 
which to me seem to make them most unsuitable for such 
purposes. ; 
The opinions I hold on this subject may not be generally 
applicable to all the formations, nor do I claim that they are, 
but they certainly apply to the Carboniferous formation, and 
it is only in connection with Carboniferous rocks that I can 
personally speak. | 
One concrete example may illustrate why, in Carboniferous 
rocks, the Mollusca are not so suitable as plants for deter- 
mining horizons. 
When sinking the shaft of the Hamstead Colliery, Great 
Barr, near Birmingham, 450 feet of red and purple shales, 
marls, and sandstones were passed through before meeting 
with the Middle Coal-Measures. These upper rocks had been 
mapped by the Geological Survey as Permian; but, from the 
evidence derived from the plants, which were carefully 
collected by Messrs F. G. Meacham, M.E., and H. Insley, 
who were in charge of the work, it was shown that these 
shales belonged to the Upper Coal-Measures.? 
The Mollusca met with were also preserved, though un- 
fortunately some of the specimens collected were destroyed 
through an accident. From those preserved, Dr John Young 
identified the following :— 
1 Pext-Book of Geology, 2nd ed., p. 601. 
* See Trans. Roy. Soc. Edin., vol. xxxv., p. 317, 1888, 
