Related Geological Conditions 31 



of land devoid of cold mountain areas, and of seas devoid 

 of dark ocean depths, formed the most wide-spread and 

 favorable environal conditions for active organic evolution. 



Geologically then the writer would consider that great 

 masses of rock strata of Upper Silurian, of Devonian, and 

 of Carboniferous age are of freshwater origin, and that 

 these in many cases equal or excel rocks that are clearly 

 of marine origin. Thus the Scottish deposits described by 

 Campbell in Kincardineshire (/-/; 923), the corresponding 

 Downtonian beds of Central England, the Niagara and 

 Waterlime strata of North America, those of Oesel in 

 Russia, also some Swedish beds are largely or wholly fresh- 

 water. The extensive deposits of Old Red or Devonian 

 rocks over the Northern United States and Southern 

 Canada, over North and Central Scotland, Ireland and 

 some parts of England, those of Russia and Germany also 

 are of similar origin. Some of the Lower Carboniferous 

 or Misslsslpplan of North America, the Calciferous of 

 Central Scotland the Culm of Austria and parts of 

 Germany, as well as the greater extent of the enormous 

 deposits that make up the True Coal Measures of North 

 America, of Europe, of parts of Asia and of Australia 

 should be similarly classified. 



The truth of the above Is In part proved by the habitual 

 absence of marine organisms; by the uniform presence of 

 a biological assemblage that Is treated of In detail In some 

 succeeding chapters; by the frequent direct continuity in 

 structure, in mode of life, and In habitat of such groups 

 as the Coelacanthldae, the Palaeoniscidae and represent- 

 atives of the Dipnoi (Dlpneustel) , from Devonian or 

 Carboniferous days on to Cretaceous or even recent time. 

 Abundant proof of such will be adduced later. 



It might well be objected now, that if such conditions 

 existed during palaeozoic or even more recent epochs, ex- 

 amples possibly should be left still, that would more or 

 less parallel or reproduce the above. Such seem largely 

 to be fulfilled In the group of fishes that has come down 

 from early Old Red times to our own day as the DIpneustei. 

 The three living genera and all the species of these, inhabit 

 wide areas of South America, of West and Central Africa, 



