1870.J The Bate of Geological Change. 323 



In his Anniversary Address to the Geological Society last year, 

 Professor Huxley defined a " third phase of geological speculation, 

 namely, Evolutionism." This doctrine, in the words of the author, 

 " emhraces all that is sound in both Catastrophism and Uniformi- 

 tarianism, while it rejects the arbitrary assumptions of the one, and 

 the, as arbitrary, limitations of the other." To my mind it cannot 

 well be distinguished from ordinary Theoretical Geology, unfettered 

 by the trammels of any school ; but obviously, the Evolutionist is 

 prepared to accept whatever theory on the rate of geological change 

 can be shown to be consistent with those known facts which can 

 fairly be quoted as evidence. 



The title of this article is capable of more than one interpreta- 

 tion, and in its various meanings it has already been investigated 

 by speculative geologists. The late Professor Edward Forbes, in 

 his lecture before the Royal Institution, " On the Manifestation of 

 Polarity in the Distribution of Organized Beings in Time,"* en- 

 deavoured to show that the rate of development of generic types 

 reached its maximum intensity, firstly, during the earlier Palaeozoic 

 periods, and secondly, during the later Neozoic periods; that is to 

 say, near the beginning and the end of the geological scale. Again, 

 the rate of development was shown to be at its minimum during 

 the later Palaeozoic (Permian) and earlier Neozoic (Triassic) periods, 

 from which contiguous zero-points the development of generic types 

 was asserted to increase in both directions.! This relation Professor 

 Forbes termed " Polarity," and he showed how in several of the 

 great divisions of the animal kingdom, two of their groups appeared 

 to exercise a kind of " reciprocity," as, for instance, our old friends 

 the Palaeozoic four-starred corals versus the Neozoic six-starred. 

 But Professor Forbes was careful to make the reservation that 

 " the numbers of species in a group or genus at anjr given epoch is 

 to be excluded, not being an element in the discussion of the ques- 

 tion, though apt to be introduced through mistake of the nature 

 of the generalization attempted to be attained." Indeed, the rela- 

 tions of individuals, species, and genera were favourite subjects of 

 speculation with this poetic and philosophical palaeontologist ; and 

 the generalization we have just sketched was a sequel to some 

 other inquiries, in recording which he defines a genus as " an 

 abstraction — an idea — but an idea impressed on nature, and not 

 arbitrarily dependent on man's conceptions. "J Again, " a genus 

 consists of more or fewer of these manies resulting from one 

 [species] linked together, not by a relationship of descent, but by 



* 'Notices of the Meetings of the Royal Institution,' vol. i., p. 428. 



t This view may be correct ; but at present, as at the time when it was 

 advanced, we have only negative evidence in support of it ; and it is still very 

 possible that Permian and Triassic rocks,, rich in generic types, may be discovered 

 in some hitherto unexplored region of the earth. 



% 'Notices,' &c, vol. i., p. 196. 



