——— 7." 
Geological Society of London. 123 
generic intensity) which are characteristically paleozoie, 7. ¢., 
have their maximum development and variety during the pa- 
leozoic epoch, or else are even exclusively palozoic. 
6. The majority of generic ideas that originated during 
the neozoic epoch, belong to groups which are characteristi- 
cally neozoic in the same manner. 
7. The minimum development of generic ideas in time is 
at or about the passage or point of junction of the palzozoic 
and neozoic epochs. 
8. Groups characteristically palzozoic swell out, as it were, 
in a direction towards, not from, the commencement of the 
palzozoic epoch. 
9. Groups characteristically neozoic swell out in a direc- 
tion from the commencement of the neozoic epoch. 
That there are apparent exceptions to these general facts 
I do not pretend to deny; but the rules are so much more 
powerful than the exceptions, that we may safely wait with 
confidence for the explanation of the seeming anomalies dur- 
ing the course of the progress of research. 
Now there is but one conclusion that can be drawn from 
these facts, if after being tested with every evidence now 
known to us, they remain intact as our science progresses. 
This conclusion is to the effect, that the relation between the 
palzozoic and neozoic life-assemblages is one of development 
in opposite directions, in other words of Polarity. In the 
demonstration of this relation, it seems to me that we shall, 
in all probability, discover the secret of the difference be- 
tween the life anterior to the Trias and the life afterwards. 
The notion is in some degree a metaphysical one, but not the 
less capable of support through induction from the facts. I 
plead for its consideration, believing it to be worthy of ear- 
nest inquiry. I know that its novelty and seeming vague- 
ness may repel many when it is thus briefly, and as if in out- 
line, put forth. But before any geologist or naturalist rejects 
it, 1 would ask him to study carefully the admirable mono- 
graphs, written without a bias, of whose merits I have been 
discoursing in this Address ; to seek out the manifestation of 
the idea, in the first instance, in some important and charac- 
teristic group of beings about whose time-distribution we 
