276 STEATIGKAPH1CAL GEOLOGY 



Mr. Salter compared them with, those of Pembrokeshire in 1863, 17 

 but his opinion was that the Pilton Beds included the equivalent 

 of the lower limestone shale. He says, " Nearer Barnstaple these 

 Pilton Beds begin to trough small patches of a barren softer slate 

 which is only seen well developed south of Pilton and occupying 

 the lower ground east and west of Barnstaple." In these soft slates 

 the prevalent fossils are Phillipsia seminifera, Spirifer bisulcatus, 

 S. laminosus, S. cuspidatus, Productus Martini, Orthis Michelini, 

 and other exclusively Carboniferous species. 



Shales with a similar set of fossils occur at Fremington 

 west of Barnstaple, and are succeeded by the Coddon Hill Beds 

 consisting of shales and chert-beds ; the shales yield the Goniatites 

 characteristic of the lowest Pendleside Beds, i.e. Prolecanites com- 

 pressus, P. mixolobus, and Nomismoceras spirorbis, and the cherts 

 contain Radiolaria. They are overlain by black shales con- 

 taining Posidonomya Becheri, and black limestones with the same 

 fossil. 18 



The combined thickness of all these beds is not very great, 

 apparently not more than 400 to 500 feet, unless a portion of the 

 Pilton Beds is included, and it is impossible to regard them as 

 representing the whole Avonian succession. From the fossils above 

 quoted it looks as if the base and the upper portion of the normal 

 sequence were present, and it is possible that the central beds are 

 cut out by faulting, for the boundary of the Pilton Beds at and 

 east of South Molton is believed to be a fault. 



In South Devon and Cornwall nothing comparable with the 

 Pilton or with the Fremington Beds has yet been found. The 

 lowest Carboniferous Beds are either unconformable to or faulted 

 against the highest Devonian rocks ; but the cherts and limestones 

 of the Coddon Hill Group are well developed and appear to be 

 rather thicker than in North Devon. West of Dartmoor they are 

 associated with lava- flows, and the general succession according to 

 Mr. Reid is as follows : 19 



Feet. 

 Upper lava of Brent Tor, etc. . . . about 150 



Beds of Radiolarian chert 

 Black shales and lenticular limestones 

 Lower lavas ..... 

 Hard black shale and chert-beds 



70 

 250 



50 

 150 



I have elsewhere 20 suggested that the break which here seems to 

 exist between the Devonian and Carboniferous Systems may be a 

 result of the volcanic action indicated by the presence of the lavas 

 and by the intrusive mass of Brent Tor, which is supposed to have 

 been a volcanic vent. The sea-floor may have been slowly raised 



