7 
, 
Pe et 
Geological Society of London. 119 
only slightly more, than the degree of difference between the 
lower and upper sections of the great mesozoic period. But 
the gap between paleozoic and mesozoic, although the link 
be not altogether broken, is vastly greater than any other of 
the many gaps in the known series of formations. I am one 
of those who hold, a priori, that all gaps are local, and that 
there is a probability at some future time of our discovering 
gradually somewhere on the earth’s crust evidences of the 
missing links. All our experience and knowledge, theoretical 
and practical, warrant the affirmation that at every known 
stage of geological time there were sea and land. Even those 
who believe in a primeval azoic period will hardly sanction 
the supposition that there has been any repetition of azoic 
epochs since the first life-bearing era commenced. And if so, 
and if there were always sea and land since the commence- 
ment of the first fossiliferous formation, we are warranted 
In assuming that both earth and water had their floras and 
their faunas. All geological experience goes to shew that 
wherever you have a perfect sequence of formations accu- 
mulating in the same medium, air or water as the case may 
be, there is, if not a continuance of the same specific types, 
a graduated succession and interlacement of types and of the 
facies of life-assemblages : even as on the present surface of 
the earth the faunas and floras of proximate provinces inter- 
mingle more or less specifically, or, if physical barriers pre- 
vent the diffusion of species, assume more or less one gene- 
ral facies. This passage, by aspect and type, of one stage in 
time into another is but scantily indicated at present in the up- 
permost manifestations of the paleozoic life and the lowermost 
of the mesozoic. The missing links will sooner or later re- 
ward the diligence of the geological explorer. 
But, in the general aspect of the paleozoic world, con- 
trasted with the worlds of life that followed, although all are 
evidently portions of one mighty organic whole, there seems to 
me to be something more than the contrast that depends on 
the loss or non-discovery of connecting links. There is more 
than we can explain by thistheory. Granting for its support 
all facts capable of being so applied, there are residual phe- 
