1866.] JUKES — OLD EED SAXDSTOI^-E AND DEVOKIAN". 361 



the Irish Old Eed Sandstone being the same as that of South Wales, 

 but more indurated and traversed by slaty cleavage. If that judg- 

 ment be a correct one, it follows, that as the Carboniferous Slate of 

 Ireland is, without doubt, above the Old Eed Sandstone, the Old 

 Eed Sandstone striking from Pickwell Down to Haddon Down will 

 be below the rocks of Lynton, all appearances to the contrary not- 

 withstanding ; and that consequently some great fault, with a down- 

 throw to the north, must run between the two, as suggested in 

 fig. 17. The alternative to the conclusion will be, that there is a 

 band of rocks, from 3000 to 7000 feet in thickness, precisely re- 

 sembHng the Irish Lower Group, but lying in Devonshire in the 

 middle of the Upper Group. If there were any direct evidence in 

 Devonshire that such is the structure of the country, all that could 

 be said would be, that it was a very remarkable, and, as far as I 

 know, unexampled occurrence. There is, however, no direct evi- 

 dence for it beyond the general southern dip of the country, which 

 is just as compatible with one hypothesis as the other. There is no 

 place that I could find, either by my own search, or described in any 

 published researches of others, where the band of slates stretching 

 from Mortehoe to Exton can actually be seen to pass under the red 

 sandstones and slates that stretch from Pickwell Down to Haddon 

 Down; they can only be seen to dip towards them. 



10. ThicJc7iess of the rocks of North Devon on the ordinary hypo^ 

 thesis. — There is even a strong presumption against the ordinary 

 hypothesis to be deduced from the enormous thickness which it com- 

 pels us to assign to the rocks of North Devon, and that without 

 arriving at any definite base to them. All observers, from Sectgwick 

 and Murchison, Weaver*, De la Beche and Phillips, down to our 

 own day, when the Eev. M. Mules, of Marwood, and my colleague, 

 Mr. Etheridge, who have constructed rough maps of the country f, 

 and Mr. Townshend M. Hall, of Pilton, who has described it to the 

 Exeter Naturalists' Eield Club:]:, agree in the opinion that there is a 

 regular succession of rock-groups, dipping one under the other, from 

 Lynton to the latitude of Barnstaple Estuary and South Molton. 



Mr. Weaver, the accuracy of whose observations no one has ever 

 disputed, divides the rocks of the country into eight such groups, as 

 follows : — 



8. Culmiferous Shales. 1 r i f f 



7. WaveUite schistus and limestone. J '"^^^ ®^^'^^^' 

 6. Trilobite slates. 



5. WooUacombe sandstones, flags, and slates. 

 4. Morte slates. 



3. Trentishoe quartzy-slate and sandstone, including tlie 

 Combe-Martin limestones. 



2. Lynton calcareous slates. 



3 . Eoreland sandstones (top of Old Eed Sandstone ?). 



* See Proceedings of Geol. Soc. London, vol. ii. p. 589, Jan. 3rd, 1838. 

 t I am indebted to both these gentlemen for a sight of these maps, 

 % Eeported in the Exeter and Plymouth Gazette, Sept. 29th, 1865. 

 VOL. XXII. — PART I. 2 G 



