IN THE CARBONIFEROUS ROCKS OF THE EDINBURGH DISTRICT. 707 



Reverting to the Estuarine fishes of the Carboniferous strata of Britain, we have seen 

 in the preceding pages how great is the difference between the species which occur below 

 and above the Millstone Grit. Only two species can with certainty be named as 

 common to the two divisions, namely, Callopristodus pectinatus and Acrolepis Hopkinsi, 

 though the list may yet be increased. For example, some of the fragmentary remains 

 of Megalichihys and Rhizodopsis which occur in the Lower Carboniferous rocks of 

 Scotland may, when more perfect material is obtained, turn out to be identical with M. 

 Hibberti and Rh. sauroides of the Coal Measures, and I may add that it is hard to dis- 

 tinguish between Sphenacanthus serrulatus of the Lower and Sph. hybodoides of the 

 Upper Carboniferous except in point of size. But the leading facts of the case would 

 still be the same. 



And the leading facts are these. 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 persist through thousands of feet of strata, and must therefore have lived for a 

 very long time without change in their specific characters. Then, after the Millstone 

 Grit, poor in fish-remains, is passed, we come to a new fauna, from which nearly all 

 the Lower Carboniferous species, and with them also a number of genera, have dis- 

 appeared, their place being taken by an Upper Carboniferous assemblage, which in its 

 main features is characteristic not only of the Coal Measures of Scotland, but of the 

 Lower and Middle Coal Measures of England, extending also into the Transition series 

 of the latter country. 



Why this sweeping change took place just about the time of the Millstone Grit we 

 do not know ; neither can we as yet explain the peculiar fish-fauna of the Lower 

 Carboniferous Estuarine beds of the South of Scotland. It remains to be seen whether 

 future investigation, for which there is abundance of room, will throw light upon those 

 questions concerning which we are at present so much in the dark. 



EXPLANATION OF THE PLATES. 



Plate I. 



General Section, of the Carboniferous Strata of the Edinburgh District, drawn up by Dr Peach, F.R.S., 

 of the Geological Survey of Scotland. 



Plate II. 



General Section of the Carboniferous Limestone Series in the Midlothian Coalfield, by Messrs Geddes, 

 Mining Engineers. Communicated to the Author by Mr H. M. Cadell of Grange. 



TRANS. ROY. SOC. EDIN., VOL. XL. PART III. (NO. 28). 5 m 



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