670 CONCLUSION. 



inasmuch as they pass into each other by indefinite gradations ; but I 

 cannot regard such varietal forms as true species. 



The relations of the Carboniferous to the Devonian flora appear 

 to militate in a positive manner against the theory of transmutation. 

 The Devonian flora of Eastern America, of which there are now known 

 nearly one hundred species, aff"ords all the principal generic forms 

 of the Carboniferous. A few of its species are identical, but the 

 greater part are distinct ; and this distinctness is even more marked 

 in the Lower Carboniferous than in the Coal formation. While, 

 therefore, a few species continued unchanged through all the vast 

 time of the Devonian and Carboniferous, others disappeared at the 

 close of the Devonian and were replaced by distinct species in the 

 Carboniferous, and all this without any material improvement or 

 elevation of type. 



It may be added, that in New York and Ohio, where no physical 

 break separates the Devonian and Carboniferous, the change of flora 

 takes place in the same manner, and that the floras of the Devonian 

 and Carboniferous are now too well known, and that over too large 

 an area to allow us to explain this by " imperfection of the record." 



Again, if we turn to the Primoi'dial fauna of St John, we find there, 

 as in similar horizons in Europe, several distinct types of animal exist- 

 ence already well defined, and none of them pointing by any character 

 to the primitive Eozoon of the Laurentian rocks, which stands out as 

 distinctly by itself as the two little land-shells of the Coal measures. 



On the great question at issue between the " Uniformitarians" and 

 " Catastrophists," I desire to occupy that middle ground to which I 

 am glad to see that Lyell and Mui'chison, the two great leaders of 

 geological opinion in Great Britain, tend in their later works. AVhile 

 the doctrine of the absolute unifomiity of natural laws cannot be too 

 strongly held, we must admit that periods of more and less energetic 

 action of the great causes of geological change have alternated with 

 each other over regions so extensive as practically to aflect the whole 

 world, and that tlie period of human observation has been probably 

 too limited to enable us fully to appreciate the extremes of these 

 oscillations. In other words, the long-continued operation of uniform 

 causes, whether geological or astronomical, may lead to an accumula- 

 tion of effects in certain directions, terminating in a change, cataclysraal 

 in its character, and initiating a new train of causes perhaps under 

 very different conditions. It is true that such a cataclysm may, in 

 a broader view, be regarded as a part of the uniform order, just as a 

 thunderstorm or an earthquake may be regarded as an eff'ect of regular 

 natural laws, as much as a tide or a current. Still we should beware 



