A. J. Jukes-Browne — Loiver Carboniferous in Devon. 357 



But even if there wei'e no active vents in the northern area we 

 must remember that the distance between the two areas is not great. 

 The tract of Lower Culm at and near Bampton is only 24 miles 

 north of Ashton, and Coddon Hill is only about the same distance 

 from the northern border of Dartmoor, so that if the southern area 

 was being elevated and shallowed the northern area could hardly 

 fail to partake in the upward movement to some extent. 



The great thickness of the Upper Devonian in North Devon does 

 indeed seem to indicate that no upward movement was in progress 

 there during the process of its formation, and in this connection we 

 must remember that we have no proof of upheaval at this time 

 in South Devon, only the association of volcanic rocks. The actual 

 uplift may not have taken place until the beginning of Carboniferous 

 time, for it is only in the Lower Culm that evidence of erosion occurs, 

 and it is the Lower Carboniferous rocks which are apparently 

 so thin both in South and North Devon. 



The probability of the suggested upheaval and erosion in South 

 Devon is increased by the fact that in Brittany (still further south) 

 there is a decided break between the Devonian and the Carboniferous. 

 In that region the oldest Carboniferous rocks are conglomerates, 

 sandstones, and volcanic rocks, which lie unconformably upon the 

 Middle Devonian, both in the basin of Chateaulin and in that of 

 Laval. These are succeeded by slates with occasional limestones, 

 which seem to represent the Visean or upper part of our Limestone 

 Series.^ 



In conclusion, I may observe that I should not regard the existence 

 of Eadiolaria in the chert-beds as constituting a difficulty in the 

 way of my suggestion, for I dissent from the view that Eadiolarian 

 cherts are by themselves any proof of deep water. Mr. L. Cayeux 

 has shown that siliceous deposits containing Eadiolaria occur in the 

 Oxfordian of the Ardennes, in the Gaize de I'Argonne, in the 

 Smectique de Herve (Belgium), and in the Lower Eocene tufifeaux 

 of France and Belgium. None of these can be regarded as specially 

 deep-water deposits, while the last occurs in sands of the age of our 

 Thanet Beds, and yet is very rich in Eadiolaria.'- 



It is evident from these facts that other proofs than the mere 

 occurrence of Eadiolaria are required before the supposition of very 

 deep water or oceanic conditions can be accepted. Such proofs are 

 not forthcoming in the case of the Culm chert-beds, for, as I have 

 remarked elsewhere,^ the beds associated with them are not 

 comparable in any way to the oceanic deposits of the present day. 

 So far as we can judge, Eadiolarian deposits are more indicative of 

 conditions which do not favour the existence or the preservation of 

 the remains of calcareous organisms than of any special depth of water. 



Finally, the fact of the occurrence of similar cherts containing 



1 See de Lapparent's Traite de Geologie, 4tli ed., p. 895, and references. 

 - Contrib. a I'etude micro, des terr. sedim. : Mem. Soc. Geol. ISTord, torn, iv, 

 Lille, 1897. 

 ' StratigrapMcal Geology, p. 269, Stanford (1901). 



