274 peof. e. hull on the geological relations 



Sfccessive Physical Phases. 

 It would appear from the above, that at the close of the Upper- 

 Silurian period, represented in Ireland by the Glengariff beds, in 

 Wales by the Upper Ludlow and Passage-beds, and in Scotland by 

 the Lower Old Red Sandstone, there was a general elevation 

 of all the northern and western portions of the British Isles, ac- 

 companied by flexuring of the strata, and followed by extensive 

 denudation. In the area of the south of England, however, and 

 adjoining continental districts it was otherwise. Here there was, 

 on the contrary, continuous depression ; and the sea overspread this 

 area, in which were deposited the Lower and Middle Devonian beds. 

 With the Upper Devonian stage, or Old lied Sandstone proper, the 

 submersion of the western and northern portions of the British Isles 

 began. Lacustrine conditions were established over the south of 

 Ireland, portions of Scotland, and the north of Ireland. In the 

 waters of these lakes the Old Eed Conglomerates and succeeding 

 beds with Anodonta were laid down ; after which, by a further 

 general subsidence, at the commencement of the Carboniferous 

 period the sea-waters flowed in, establishing themselves over all 

 the lower regions, and prevailing generally throughout the lower 

 and middle stages of that formation. 



General Deductions. 



If the above views and arguments be correct, it follows : — 



1st. Thaf there is only one formation which can properly be 

 termed the '* Old Eed Sandstone." This is represented in Devon- 

 shire by the Upper Devonian Sandstone of Piekwell Down, by 

 the Old Eed Sandstone and. Conglomerate (including the Kiltorcan 

 beds) of the south of Ireland, the Upper Old Eed Sandstone of 

 Scotland, and the Psammite du Condroz of Prance and Belgium. 



2nd. That the so-called '^ Lower Old Eed Sandstone " of Scotland 

 is the lacustrine representative of the Uppermost Silurian beds of 

 the English and Welsh borders, and of the Glengariff beds of the 

 south of Ireland, and forms the connecting link between the Silu- 

 rian and Devonian formations. 



3rd. That the hiatus between the " Upper " and " Lower Old 

 Eed Sandstone " of Scotland, and between the Old Eed Sandstone 

 and Glengariff beds in Ireland is filled up in Devonshire by the 

 Middle and Lower Devonian formations. 



4th. And, assuming that the Eoreland grits are (in part) the 

 equivalents of the Upper Ludlow rocks on the one hand, and of the 

 Glengariff beds on the other, it would appear that all over the 

 British Islands, except the south of England and the Welsh borders, 

 land-conditions prevailed from the close of the Upper Silurian stage, 

 throughout the Lower and Middle Devonian stages ; at the close of 

 which there was a general re-submergence, with the formation of 

 lakes and estuaries, during the Upper Devonian or Old Eed Sand- 

 stone period. These lakes and estuaries were overspread by the 

 waters of the sea at the commencement of the Carboniferous 

 period. 



