596 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. 



tion as those of the parallel range of Pickwell, Dulverton, and 

 Main Downs, &c. ; and the Lynton and Ilfracombe slates, that rest 

 upon the Foreland sandstones, are therefore made to be of the same 

 age as those of Baggy, George Ham, Marwood, Sloly, and Brushford, 

 &c., on the south of the upper range of Old Red Sandstone above 

 mentioned. Prom these views of Professor Jukes I entirely differ, 

 both as to his premises and his conclusions, relative to the Devonian 

 question, differing from him in the reading of the structure of the 

 typical Devonian country, and also upon palEeontological grounds. 



Similarity is not identity ; and however much certain portions of 

 these slates and grits may resemble each other in some few external 

 features, yet between the Baggy and Croyde slates and those of 

 Lynton and Ilfracombe there is on the whole a most strongly 

 marked difference, both in physical structure and organic contents ; 

 indeed no two groups of slate rocks, when minutely examined, differ 

 more, as a mass, or amongst themselves, than those ander discus- 

 sion, which occupy the country extending from Lynton on the north- 

 east to Pilton and Barnstaple on the south-west; and no more 

 striking contrast amongst a slaty group can be determined than 

 between those fissile and calcareous sandstones that occur be- 

 tween the Lower red sandstones of the Poreland series and the 

 Upper red sandstones of Pickwell Down (in Morte Bay), which con- 

 tinuously strike across the country to Wiveliscombe. 



There is no resemblance between the fissile beds of the southern 

 area and those of the northern, i. e. taking the hne of Upper E,ed 

 Sandstones of Pickwell as our east and west line of demarcation. 

 The great group of unfossiliferous slates of Mortehoe, Lee, &c., of 

 peculiar physical structure and some 5000 feet thick (and not known 

 to the south), exists at the base of the Pickwell sandstones, and has 

 to be accounted for through either of the hypotheses put forward, viz. 

 that " of a downthrow fault to the north, or an anticlinal line across 

 the country," neither of which can account for the total loss of these 

 slates, or of the thick slates and associated limestone of the Ilfra- 

 combe series, or the second series of red sandstones below them, 

 and capping the hills above the Valley of Eocks at Brendon, above 

 Watersmeet, and constituting also the thick red and grey grits 

 of Woodabay, Martinhoe, Trentishoe, Heddon's Mouth, and the two 

 Hangman Hills, all on the north side of this supposed fault, and 

 overlying the Lynton fossiliferous slates, which, as before stated, 

 repose upon the Poreland and Countesbury red sandstones. In 

 fossil- evidence, also, we have an equal discrepancy, or an amount of 

 difference alone sufiicient to cause a doubt respecting the identity of 

 the age of the rocks of the two areas, and to show conclusively that 

 there is an ascending order or sequence in the rock-masses of IN'orth 

 Devon, as well as in their fauna, and that we should reasonably 

 expect that many species occurring in rocks of older age, or in 

 the Lower and Middle Devonian groups, should continue to live on, 

 and either die out or migrate to other areas or provinces, if the 

 conditions favourable to their prior existence changed. 



2. Foreland, east of the River Lynn. — Immediately east of the river, 



