CONCLUSION. G69 



I would also invite the attention of geologists to the doctrine of 

 equivalent geological cycles, as stated in that chapter; believing that, 

 in spite of all local diversities, such general cycles of geological change 

 will at length be fully established. For the present, I am aware that 

 there is a tendency among some of the younger geologists to extend 

 to the whole world, and to all time, the exceptional coast-conditions 

 of small areas, and very limited faunas ; but this attempt to raise the 

 exceptions to the rank of the rule cannot deceive those whose studies 

 have made them familiar with the enormous areas of deposition and 

 life-distribution in the modern ocean, and with the still more uniform 

 conditions of the Palaeozoic land and sea. 



With respect to theories of metamorphism and the production of 

 what have been termed " Indigenous " crystalline rocks, the pheno- 

 mena observable in Acadia point out that the heat of the great igneous 

 masses of the interior of the earth's crust has been mainly instru- 

 mental in effecting such changes, though much must be allowed for 

 the original chemical differences of the beds. There is also very 

 striking evidence of the power of huge Plutonic masses to melt their 

 way, if we may so speak, through the aqueous beds, with very little 

 mechanical disturbance, and only a limited amount of metamorphism 

 in the immediate vicinity of such masses. Nor can there be any 

 question that the igneous masses themselves have been much modified 

 in their chemical constitution by beds through which they have 

 passed, so that there is a certain correspondence between the character 

 of igneous rocks and that of the beds which they penetrate. In 

 addition to all this, we have bedded traps and tufaceous beds composed 

 of the debris of igneous rocks, readily assuming under metamorphism 

 the aspect of Plutonic dykes. It is clear that a want of careful 

 analysis of facts so complicated may readily lead to the confused and 

 contradictory doctrines on the relations of the metamorphic sedi- 

 ments and the " exotic " Plutonic rocks now too prevalent. 



I have not been able to find, in the remarkably complete scries of 

 fossils afforded by the Carboniferous of Nova Scotia, any evidence of 

 the gradual transmutation of species by natural selection or any other 

 cause. On the contrary, species appear without any manifest cause, 

 and remain unchanged, or with very limited varietal modifications 

 during very long periods. I admit, however, that in the case of cer- 

 tain species of wide range and long continuance, as Productus cora 

 and Alethopteris loncliitica, for example, varietal forms can be observed 

 to be characteristic of certain places and beds ; and that if we were to 

 regard the varieties as species, and the latter as sub-genera, then such 

 supposed species might be regarded as transmutable into each other, 



