272 TROr. E. HULL ON THE GEOLOGICAL RELATIONS 



remains. Out of a list of between 50 and 60 species enumerated 

 bj^ Prof. Geikie from " the Lower Old Eed Sandstone " of the north 

 of Scotland (Lake Orcadie), not one occurs in the Upper Silurian 

 beds, according to Sir R. Murchison*. But it should be recollected 

 that, according to Professor Geikie's own showing, the northern 

 basin was completely isolated from that of the borders of Wales 

 (the Welsh lake), which, as I have hinted, was rather in all pro- 

 bability an estuary opening out upon the sea in the direction of 

 the Bristol Channel, Devonshire, and the south of England, which 

 would sufficiently account for the complete dissimilarity in the ich- 

 thyic fauna of the two regions. Comparing the list given by Sir R. 

 Murchison with that of Mr. Etheridge, however, I find that in other 

 districts the following seven species are common to "the Lower 

 Old Red, and the Ludlow and Passage-beds," viz. AucJienasjns 

 Salteri, Egert., CeiDlmlaspis Murchisoni, Egert., C. omatus, Egert., 

 OncJiiis Murchisoni, Ag., Pteraspis Banksii, Huxl. & Salt., Pt. trun- 

 catus, Huxl. & Salt., and Pt. Lhydii, Ag. Several genera of crus- 

 taceans are also common to both. 



Erom these considerations I draw the conclusion that there is 

 really in the British Isles, as elsewhere, only one formation of "Old 

 Red Sandstone " properly so called — namely the upper member of 

 that name in Scotland, the yellow sandstone and conglomerate 

 below the Carboniferous Limestone of South "Wales and Hereford, 

 the Pickwell-down sandstone of Devonshire, and the Old Red Sand- 

 stone and conglomerate of the south of Ireland. It would also 

 appear that " the Cornstone group " are not the representatives of 

 the "Lower Old Red" of Scotland, but of the Middle Devonian 

 and part of the Lower Devonian beds of Devonshire and the Conti- 

 nent; while "the Lower Old Red " of Scotland is the lacustrine 

 equivalent of the Uppermost Silurian beds both of Herefordshire and 

 of the south of Ireland, namely the Glengariff or Dingle beds. 

 These seem to me the logical conclusions to be drawn from the facts 

 and arguments stated in this paper. The following table will pre- 

 sent the above conclusions in a condensed form : — 



* ' Siluria,' 4th edit. p. 536. Compare with Geikie's list supra cit, p. 452. 



