214 CRITIQUES AND ADDRESSES. [ix. 



have left its remains in the Coal-measures, especially as 

 there is now reason to believe that uiuch of the coal was 

 formed by the accumulation of spores and sporangia on 

 dry land. But if we consider the matter more closely, 

 I think that this apparent objection loses its force. It is 

 clear that, during the Carboniferous epoch, the vast area 

 of land which is now covered by Coal-measures must 

 have been undergoing a gradual depression. The dry 

 land thus depressed must, therefore, have existed, as 

 such, before the Carboniferous epoch in other words, 

 in Devonian times and its terrestrial population may 

 never have been other than such as existed during the 

 Devonian, or some previous epoch, although much higher 

 forms may have been developed elsewhere. 



Again, let me say that I am making no gratuitous 

 assumption of inconceivable changes. It is clear that 

 the enormous area of Polynesia is, on the whole, an area 

 over which depression has taken place to an immense 

 extent ; consequently a great continent, or assemblage 

 of subcontinental masses of land, must have existed at 

 some former time, and that at a recent period, geologically 

 speaking, in the area of the Pacific. But if that con- 

 tinent had contained Mammals, some of them must have 

 remained to tell the tale ; and a it is well known that 

 these islands have no indigenous Mammalia, it is safe 

 to assume that none existed. Thus, midway between 

 Australia and South America, each of which possesses an 

 abundant and diversified mammalian fauna, a mass of 

 land, which may have been as large as both put together, 

 must have existed without a mammalian inhabitant. 

 Suppose that the shores of this great land were fringed, 

 as those of tropical Australia are now, with belts of 

 mangroves, which would extend landwards on the one 

 side, and be buried beneath littoral deposits on the other 

 side, as depression went on ; and great beds of mangrove 



