612 PROCEEDINGS OF THE GEOLOaiCAL SOCIETY. 



•where casts of Mycdinci, Favosltes cervicornis, Oacullcea, MacrocheUus 

 hrevis, Sangidnolaria &c., and Natlca are found ; these sandstones 

 and their fossils, however, graduate insensibly into the red and grey 

 slates with String ocephalus Burtini in Combe Martin Bay. I there- 

 fore place them at the base of the Middle group as the Middle E-ed 

 Sandstones, the marine Middle Devonian slates being conformable 

 upon them. 



(2) These red gritty sandstones constitute a great belt of country, 

 three miles in width, from Trentishoe and West Challacombe on the 

 west, to Croydon Hill in "West Somerset, on the east, the beds at 

 Timberscombe being lowest, and those of Ashwell the highest ; few 

 fossils are known to occnr in these sandstones along this strike of 

 thirty miles; they divide the lower or Lynton slates from the 

 Middle or Ilfracombe ; and the base and top are conformable to the 

 Lower slates of Lynton on the one hand, and the Middle or Ilfra- 

 combe above on the other. Their thickness is from 1500 to 2000 feet. 



(3) Eesting upon this extensive series of red sandstones (Middle 

 Old lied) and along the meridian of "West Challacombe, Paracombe, 

 Black Barrow Down, Ashwell, Luxborough, and iNTettlecombe, as 

 their northern base, are the argillaceous and calcareous slates of the 

 Middle Devonian or Ilfracombe gronp, its lower half containing a 

 fine and marked assemblage of fossils, its upper half being entirely 

 iinfossiliferous and ending at its junctio^i with the Pickwell Down 

 Sandstones, along a line fromWoolacombe, at Morte Bay, to the north 

 of Main Down near Wiveliscombe on the east, and almost parallel to 

 the base-line above named ; this series, although much rolled and 

 contorted, chiefly with the dij), passes conformably or nnfaulted 

 (along the line described) under the Upper Old Eed Sandstone of 

 Pickwell, Pavisham, and Garmond Downs, Span Head, and Heydon 

 and Main Downs. This zone or series of slates, grits, and limestones 

 together is at least 8000 feet thick. 



(4) The npper half of the Middle or Ilfracombe series of slates is 

 Iinfossiliferous. They are finely exposed at Lee Bay, Rockham Bay, 

 and Morthoe, and stretch across the whole of Korth Down, from 

 Morte Bay to the Oakhampton Quarries, north of Wiveliscombe; their 

 physical characters are persistent throughout this strike ; they every- 

 where underlie the upper ^one of red sandstones, the ''Old Eed Sand- 

 stone " of Prof. Jukes, and are conformable to the base of it. Their 

 thickness cannot be less than 3500 or 4000 feet *. 



■ Y. Pal^ontological Value oe the Oeganic Eemains eound in 

 THE Devonian Geoups. 



I have now to examine, estimate, and coordinate the values of the 

 Devonian groups, separately and collectively, as one great system, 

 both in Great Britain and Europe, especially in those areas where 



* In this communication I do not enter into details relative to the Upper 

 Devonian beds. This has been done for that gronp south of Pickwell Down by 

 Mr. Salter. It would only be repeating his views in detail to do so. Vide 

 Quf.rt. Journ. Geol. Soc. vol. xix. 1863. 



