350 THE LAW OF EVOLUTION CONTINUED. 



not a single totally extinct class; and of the orders, at the 

 outside not more than seven per cent, are unrepresented in 

 the existing creation " if he urges that among these some 

 have continued from the Silurian epoch to our own day with 

 scarcely any change and if he infers that there is evidently 

 a much, greater average resemblance between the living 

 forms of the past and those of the present, than con- 

 sists with this hypothesis; there is still a satisfactory 

 reply, on which in fact Prof. Huxley insists; namely, that 

 we have evidence of a " pre-geologic era " of unknown du- 

 ration. And indeed, when it is remembered, that the enor- 

 mous subsidences of the Silurian period show the Earth's 

 crust to have been approximately as thick then as it is now 

 when it is concluded that the time taken to form so thick 

 a crust, must have been immense as compared with the time 

 which has since elapsed when it is assumed, as it must be, 

 that during this comparatively immense time the geologic 

 and biologic changes went on at their usual rates; it be- 

 comes manifest, not only that the palaeontological records 

 which we find, do not negative the theory of evolution, 

 but that they are such as might rationally be looked for. 



Moreover, it must not be forgotten that though the evi- 

 dence suffices neither for proof nor disproof, yet some of its 

 most conspicuous facts support the belief, that the more het- 

 erogeneous organisms and groups of organisms, have been 

 evolved from the less heterogeneous ones. The average 

 community of type between the fossils of adjacent strata, 

 and still more the community that is found between the 

 latest tertiary fossils and creatures now existing, is one of 

 these facts. The discovery in some modern deposits of such 

 forms as the Palseotherium and Anaplotherium, which, if 

 we may rely on Prof. Owen, had a type of structure inter- 

 mediate between some of the types now existing, is another 

 of these facts. And the comparatively recent appearance 

 of Man, is a third fact of this kind, which possesses still 

 greater significance. Hence we may say, that though our 



