HUGHES : DsGLEBOROUGH. 
255 
the corals, or the brachiopods, or even certam genera only, 
such as Cyathophyllum or Producta, and note their range, change, 
and sometimes recurrence, in the great ascending section. This 
would be a most valuable piece of work. It would be to ajjply 
to one clear section the methods sketched out by that brilliant 
naturalist, Edward Forbes.* He points out that : — (1) Species 
of opposite hemispheres placed under similar conditions are 
representative and not identical ; (2) species occupying similar 
conditions in geological formations far apart, and which con- 
ditions are not met with in the intermediate formations, are 
representative and not identical ; (3) whenever a given assemblage 
of conditions, to which, and to which onh% certain species are 
adapted, are continuous — whether geographically or geologically 
— identical species range throughout. 
But he also explains, further on, that when forms have 
been banished from any area owing to the temporary occurrence 
of unfavourable conditions they may have lived on close by, 
and have, when favourable conditions recurred, migrated back 
into the area from which they had been driven. Perhaps, if 
it was a question of depth that influenced them, much sedimenta- 
tion may have taken place in the interval — and we shall recognise 
identical species separated by a great thickness of deposit. 
I believe that proofs of this are to be found on Ingleborough. 
That question of representative forms opens out a very 
wide field of inquiry. 
The carnivora which in one area keep down the redundancy 
of ruminants may belong to totally different genera from those 
which discharge the same function in another, and so also in 
time the fossil carnivores of any district may be quite different 
from those which Hve there now. These are representative in 
one sense. Among the lower forms of life also, at one time or 
in one area, corals or brachiopods or lamcllibranchs may pre- 
dominate and feed on lower organisms. But all of these, though 
representative in the functions they discharge, are not directly 
derived one from the other, and do not point to modification 
On the connection between the Distribution of the existing i? auna 
and Flora of the British Isles, and the Geological Changes which have 
affected their area, &c., by Edward Forbes, Mem. Geol. Survey, Vol. 1, 
p. 336. 
