| N. Devon. | S. Devon[83]. | |||
| Upper Devonian (Clymenian) |  | Pilton Beds Cucullæa (Marwood) Beds Pickwell Down Sandstone | | Entomis Slates Goniatite Limestones and Slates Massive Limestones |
| Middle Devonian (Eifelian) |  | Morte Slates Ilfracombe Beds | | Middle Devonian Limestones Ashprington Volcanic Series Eifelian Slates and Shaly Limestones |
| Lower Devonian (Coblenzian) | | Hangman Grits Lynton Slates Foreland Grits | | Lower Devonian Slates Lincombe and Warberry Grits and Meadfoot Sands |
[83] An account of the South Devon rocks by Mr Ussher will be found in the Quart. Journ. Geol. Soc., vol. XLVI. p. 487; from it the above classification of the rocks of S. Devon is taken.
The division into Lower Middle and Upper Devonian is generally adopted, though the alternative titles given to these divisions are not always used with the same signification, and the distribution of the different local stages given in the above classifications is usually adopted in the main, though a detailed comparison of the Devonian beds of North and South Devon is still attended with difficulty.
More than once an attempt has been made to prove that the apparent succession of the North Devon rocks, which is that given in the above table, is not the true one, and of recent years Dr Hicks has obtained a number of fossils from the Morte Slates which had hitherto yielded none, and he believes that these fossils indicate that the Morte Slates are on a lower horizon than the beds on which they rest. Whatever be the ultimate verdict, we can, at any rate, say that the "Devonian Question," as it is termed, is not settled[84].
[84] See Hicks, H., "On the Morte Slates and Associated Beds in North Devon and West Somerset," Quart. Journ. Geol. Soc., vols. LII. p. 254, LIII. p. 438.
Description of the Strata. The general variations in the lithological characters of the deposits of Devonian age will be seen from the accompanying figure which represents the deposits of Britain as they occurred from north to south before they had been affected by subsequent earth-movements ([Fig. 19]). The conventional signs which are used are similar to those which have been used in other parts of this work, and will save description of the section.
Fig. 19.
| A. | Lower Palæozoic and Precambrian Rocks. | ||
| N.S. | North of Scotland |  | Old Red Sandstone Type. |
| C.V. | Central valley of ditto | ||
| W. | Wales | ||
| N.D. | North Devon | | Devon Type. |
| S.D. | South Devon | ||