CHAP. V.] DEVONIAN PERIOD. 61 



proposed separate names for these basins, calling the 

 south-eastern area Lake Cheviot, the central one Lake 

 Caledonia, the small western basin Lake of Lome, and the 

 northern basin Lake Orcadie. 



From the proofs which have been adduced of the origi- 

 nal wide extension of the Old Red Sandstone (p. 52), it 

 might be thought that the three principal basins could 

 hardly have been separate lakes, but must have been inlets 

 proceeding from one large inland sea, the greater part of 

 which lay to the east of Scotland ; and, indeed, so far as- 

 the stratigraphical evidence goes this would be the most 

 natural conclusion, for the lithological differences between 

 the strata of the several basins are hardly greater than the 

 differences which exist between the Lanark and Forfar 

 types in the same Caledonian basin. The palaeontological 

 differences are, however, very much greater, the piscine 

 fauna of the Forfar and Caithness flags being so distinct 

 that Sir R. Murchison thought they could not be of the 

 same age, and was led to suggest that the Caithness flags 

 formed a middle group distinct from the Lower Old Red, 

 and of younger date than the flags of Arbroath in Forfar. 

 Dr. Geikie has shown that this is improbable, and that the 

 discrepancy is not complete, and that the general succes- 

 sion of beds in the two areas is very similar. " The 

 admitted palaeontological distinctions are probably not 

 greater than the striking lithological differences between 

 the strata of the two regions would account for, or than 

 the contrast between the ichthyic faunas of contiguous 

 water-basins at the present time." l The difference is, 

 however, sufficiently remarkable, for out of eighteen genera, 

 with sixty species from Caithness, and ten genera with 

 seventeen species from Arbroath, only four genera and one 

 or two species are common to the two areas. So great a 

 difference, though it may perhaps be lessened by future 

 1 " Textbook of Geology," first edition, p. 715. 



