140 Evolution and Distribution of Fishes 



series in the Forth basin and that of the "Culm" In east 

 central Europe as elucidated by Stur, was first indicated 

 to the writer by the veteran naturalist C. W. Peach, fully 

 forty years ago. This demonstrated an organic continuity, 

 as there doubtless was a geographic. But Heer has de- 

 scribed {gs : 161 ) an interesting set of beds in Bear Island, 

 that seem equally in their plant and animal organisms to 

 extend the Calciferous formation into far northern regions, 

 and also to relate it with the Upper Old Red of Europe 

 and Canada. 



Here it might be said that mixed or truly estuarine con- 

 ditions are of minor account and of doubtful identification, 

 though their supposed widespread existence in the past has 

 been extensively used by palaeontologists to explain puzzling 

 combinations. It is the difl^culty of reconciling such an 

 abundant fish-fauna as that of the Carboniferous system, 

 with life in wide freshwater areas, that often caused so 

 painstaking an observer as Traquair to postulate or tacitly 

 accept a marine or at least an estuarine environment, when 

 most or all of the facts in view favored a freshwater ex- 

 istence. It Is, we believe, this restricted attitude of mind 

 that caused him to think of localized estuaries, rather than 

 of connected continental masses, and so caused him to 

 overlook the great value biologically of what he so often 

 and wisely pointed out, viz. the wide distribution of some 

 species or genus over different lands, and the Invariable 

 association of such with certain phyllopods, eurypterlds, 

 scorpions, freshwater molluscs, and — not least — of like 

 genera or even species of plants. 



It Is this failure also to realize that fishes were largely 

 at this time, and previously had been wholly, land-locked 

 animals of freshwater habitat, and that were undergoing 

 wide intercontinental evolution, which caused him to pen 

 the following (77:707) : "We have in the estuarine beds 

 of the Lower Carboniferous series of the central valley 

 of Scotland, a fish-fauna of which many of the species per- 

 sist through thousands of feet of strata, and must therefore 

 have lived for a very long time without change in their 

 specific characteristics. Then, after the Millstone Grit, 



