Vol. 63.^ CARBONIFEKOUS KOCKS OP DEVON AND CORNWALL. 5 



lower beds occur along the northern and southern margins, while 

 the highest beds now remaining probably occupy a more or less 

 central position, and are exposed on the coast-line especially to the 

 south of Hartland Point. 



The general easterly and westerly strike of the rocks is well 

 seen in the disposition of the beds of coal or * culm-bands * in the 

 neighbourhood of Bideford. 1 



The rocks included within this basin are partly of Lower, and 

 partly of Upper Carboniferous age. The Lower Carboniferous 

 sequence and fauna are of great interest, and have recently attracted 

 considerable attention. 2 We are not, however, concerned here with 

 these beds, except to remark that they form, as Sedgwick & 

 Murchison 3 pointed out, less than one-tenth of the whole Carboni- 

 ferous area, the great bulk of which, as I have endeavoured to show 

 in a previous paper, 4 is occupied by rocks of Upper Carboniferous 

 age. 



The Upper Carboniferous sediments consist essentially of fine- 

 grained sandstones and alternating shales. I have been unable to 

 distinguish clearly more than one lithological type, which occurs 

 throughout the whole area as exhibited in the coast-section, 4 

 although local but impersistent variations may be found here and 

 there. Sometimes thin beds of sandstones and shales alternate, 

 fairly regularly. Here the sandstones predominate, there the 

 shales. Or thick beds of both sandstone and shale may occur in 

 the midst of thinner beds. Such changes are of frequent occurrence. 15 

 I therefore regard the whole of the Upper Carboniferous sequence 

 in West Devon and North Cornwall as forming one division litho- 

 logically, as I believe it does palgeontologically. 



These rocks are commonly spoken of as the Culm Measures, 

 a term first introduced by Sedgwick & Murchison 7 in 1837, but 

 which, as I have endeavoured to show elsewhere, 8 is of doubtful 

 advantage, in view of the faet that the German and Austrian Culm 

 is entirely of Lower Carboniferous age. The Carboniferous rocks 

 of Devon are divisible into two primary series, which are best 

 described as the Lower and Upper Carboniferous Series. 

 This view is opposed to that held by a great authority on the Devon 

 rocks, Mr. Ussher. He subdivides the Upper Carboniferous beds, 

 as developed in Devon, into two series — the Upper and Middle 

 Culm Measures, and distinguishes between these two horizons on 

 lithological grounds, as follows 9 : — 



1 These are accurately shown on the Geological Survey map of De la Beche. 



2 Hinde & Fox (95) and Wheelton Hind (04). 



3 Sedgwick & Murchison (40) p. 677. 



4 Arber (04). 



5 See also Sedgwick & Murchison (40) p. 679, andDe la Beche (39) p. 123. 



6 De la Beche (39), p. 124, arrived at the same conclusion with regard to the 

 irregular stratification of the sandstones and shales. 



7 Sedgwick & Murchison (37) p. 557. 

 s Arber (04) p. 320. 



9 Ussher (01) p. 362 & pi. xvi (map). 



