English Stratified Rocks below the Old Red Sandstone, fyc. 143 



British Isles, compares the old red conglomerates of Cumberland 

 with those on both sides of the Galloway chain. In these localities 

 they often form unconnected masses resting on the edges of the 

 greywacke; but in Galloway they are not only more largely de- 

 veloped than in the north of England, but show, as above stated, 

 many passages into the overlying carboniferous groups. 



Ireland. — He then briefly notices the sections which, in the south 

 of Ireland, connect the old red sandstone with the overlying car- 

 boniferous deposits, and form a good passage from one formation to 

 the other. The sequence is complete, and there is nothing to mark 

 any interruption of the deposits. He adopts Mr. Griffith's classifi- 

 cation, as most agreeable to the physical character of the groups and 

 to their suites of fossils. 



In the south of Ireland the lower carboniferous shales (of Mr. 

 Griffith) pass into the state of roofing- slates with a transverse clea- 

 vage, resembling the black slates at the base of the culm measures of 

 Devonshire. The great coal-field in the west of the island overlies 

 the mountain limestone ; but it puts on the form of the culm mea- 

 sures of Devon, and was formerly considered as a great transition 

 group. These facts appear to remove a difficulty in classification 

 which was presented by the mineral structure of the Devon culm 

 series. 



The author, by way of conclusion, affirms that the Scotch and 

 Irish sections enable us to show that no new formations can be in- 

 terpolated between the old red sandstone and carboniferous series, 

 inasmuch as the sequence is complete. In like manner, the sections 

 in the Silurian country show that no member is wanting between 

 the old red sandstone and the Ludlow rock. Hence he concludes 

 that, from the lower divisions of the new red sandstone down to the 

 Llandeilo flagstone, there is one continuous unbroken sequence in 

 which no term is wanting. Hence also the argument for the true 

 place of the Devonian system is complete. For any formation, with 

 fossils intermediate between the carboniferous and Silurian systems, 

 must have an intermediate position, — must therefore be on the par- 

 allel of some part of the old red sandstone, which fills that whole 

 intermediate position, But allowing the above sequence to be com- 

 plete, there may still be great difficulties in fixing the lines of de- 

 marcation by which it is to be finally subdivided. For example, the 

 lower carboniferous limestone, and the carboniferous slates of Ire- 

 land, appear to overlap and descend below the base line of the car- 

 boniferous series of England : and the same remark appears to be 

 applicable to the lowest beds of the carboniferous series of Scotland. 

 And there are similar difficulties in determining the best base line 

 for the old red sandstone, as appears from subsequent details. 



Sections of North Wales, %c. — The author next discusses two 

 sections illustrating the structure of North Wales. One is drawn 

 from the Menai Straits, in a direction about E.S.E., so as to cross 

 the Berwyn chain and end in the carboniferous series near Oswestry. 

 The other is drawn from the Berwyn chain to the carboniferous 

 limestone range on the north side of Denbighshire. The greater 



