1866.] JUKES OLD RED SANDSTONE AND DEVONIAN. 321 



III. G-eological Structure of North 

 Devon. 



1. Baggy Point to Dulverton. 



2. Dulverton. 



3. Dulverton to Dunster. 



4. Dunster to Lynton. 



5. Lynton and its neighbourhood. 



6. Lynton to Ilfracombe. 



7. Pickwell Down and Mortehoe. 



8. Aspect of the country. 



9. Probable Existence of a great East 

 and West Fault, with downthrow 

 to the Northward. 



10. Thickness of the Eocks of North 



Devon on the ordinary hypo- 

 thesis. 



11. Objections considered. 



12. Considerations on the Devonian 



Fossils. 

 IV. Appendix. 



I. Introduction. 



Haying been able during the last summer to extend a little my 

 knowledge of North. Devon, especially in the neighbourhood of Lyn- 

 ton, and having, as the result of my observations, become quite con- 

 vinced that the rocks of IS'orth Devon belong partly to the group 

 called Carboniferous Slate in Ireland, and partly to the Old Eed Sand- 

 stone, I propose to lay before the Society the grounds of that con- 

 viction. 



As I shall have to maintain that aU the first geologists of the daj^, 

 including Professor Sedgwick, Sir R. I. Murchison, Mr. Weaver, Sir 

 H. De la Beche and Professor Phillips have misunderstood the 

 structure of the country, let me hasten to avow my belief that no- 

 body whose observations were confined to Devon and Somerset, could 

 have arrived at any other than their conclusions. I fully admit that 

 the rocks near Lynton appear to be the lowest, and that there appears 

 to be a regular ascending succession of rock-groups from Lynton to 

 the latitude of Barnstaple. I am, however, compelled to dispute the 

 reality of this apparent order of succession, and to suppose that there 

 is, either a concealed anticlinal with an inversion to the north, or, 

 what I believe to be much more probable, a concealed fault running 

 nearly east and west through the centre of ISTorth Devon with a large 

 downthrow to the north, and that the Lynton beds are on the same 

 general horizon as those of Baggy Point and Marwood. As my 

 reasons for this supposition are derived from the experience acquired 

 during many years' labour in the south-west of Ireland, I must in 

 the first instance endeavour to state the result of those labours in as 

 brief a form as possible. 



It was at the close of the year 1850 that I succeeded my friend. 

 Dr. Oldham, in the Local Directorship of the Irish branch of H.M. 

 Geological Survey, when it was just entering on the examination of 

 the district alluded to. During many succeeding years the rocks 

 were patiently laid down on the six -inch Ordnance Maps by my 

 colleagues, Mr. W. L. Willson (now of the Indian Survey), Mr. 

 Andrew Wyley (who afterwards undertook the Geological Survey of 

 the Cape Colony), and Mr. G. Y. Du Noyer (now the senior Geologist 

 in Ireland). Sir H. De la Beche and Professor Edward Forbes fre- 

 quently gave their assistance to the work during those years. Sub- 

 sequently our force was strengthened by the addition of Messrs. G. H. 

 Kinahan, F. J. Foot, and Jos. O'Kelly, who still remain with us, and 

 Mr. A. B. Wynne, who afterwards left us for India. All those gen- 

 tlemen assisted in the examination of the district, and Mr. Salter 



