508 Prof. Hull — Notices of Memoirs — Dcvono- Silurian Mocks. 



III. — The Dbvono-Silubtan Formation. By Professor E. Hull, 

 LL.D., F.R.S., etc. 



THE beds which the authoi' proposed to group under the above 

 designation are found at various parts of the British Isles, and 

 to a slight extent on the Continent. The formation is, however, emi- 

 nently British, and occurs under various local names, of which the 

 following are the principal : — 



England and Wales. 



Devonshire. — 'The Foreland Grits and Slates,' lying below the 

 Lower Devonian beds (' Lynton Beds '). 



Welsh Borders. — ' The passage beds ' of Murchison, above the 

 Upper Ludlow Bone bed, and including the Downton Sandstone, and 

 rocks of the Eidge of the Trichrng. These beds form the connecting 

 link between the Estuarine Devonian beds of Hereford (generally, 

 but erroneously, called the 'Old Eed Sandstone') and the Upper 

 Silurian Series. 



South-East of England (Sub-Cretaceous district). — The author 

 assumed, from the borings at Ware, Turnford, and Tottenham Court 

 Koad, described by Mr. Etheridge, that the Devono-Silurian beds lie 

 concealed between Turnford and Tottenham Court Road on the south, 

 and Hertford on the north. 



Ireland. 



South. — ' The Dingle Beds,' or ' Glengariff Grits and Slates,' with 

 plants and fucoids, lying conformably on the Upper Silurian Beds, 

 as seen in the coast of the Dingle promontor^^ and overlaid uncon- 

 formably by either Old Eed Sandstone, or Lower Carboniferous 

 Beds ; 10,000 to 12,000 feet in thickness. 



North. — ' The Fintona Beds,' occupying large tractsof Londonderry, 

 Monaghan, and Tyrone, resting unconformably on the Lower Silurian 

 beds of Pomeroy, and overlaid unconformably by the Old Eed 

 Sandstone, or Lower Carboniferous Beds ; 5,000 to 6,000 feet in 

 thickness. 



Scotland. 



South. — Beds of the so-called ' Lower Old Eed Sandstone ' with 

 fish and crustaceans, included in Professor Geikie's 'Lake Oi'cadie, 

 Lake Caledonia, and Lake Cheviot,' underlying unconformably the 

 Old Eed Sandstone, and Lower Calciferous Sandstone, and resting 

 unconformably on older Crystalline rocks. Thickness in Caithness 

 abont 16,200 feet. 



The author considered that all these beds were representative of 

 one another in time, deposited under lacustrine or estuarine con- 

 ditions, and, as their name indicated, forming a great group inter- 

 mediate between the Silurian, on the one hand, and the Devonian, on 

 the other. He also submitted that their importance, as indicated by 

 their great development in Ireland and Scotland, entitled them to a 

 distinctive name, such as that proposed. 



