462 Notices of Memoirs — Mr, Hudlestofi's Address — 



a greater amount of comnnngling of the elements than seems to have 

 taken place. As a practical result, this discovery of a Eadiolarian 

 horizon in the Culm-measures has been of service in enabling 

 surveyors to discriminate between Devonian and Carboniferous in 

 the very obscure area on the other side of Dartmoor. This, I ventured 

 to predict, would be the case when the paper was read before the 

 Geological Society. 



The principal features of the Bristol Coalfield are too well known 

 to call for many remarks. It would seem that the Pennant rock 

 was formerly regarded as Millstone Grit, until Mr. Handel Cossham, 

 in 1864, pointed out the mistake. Mr. Wethered gave a good 

 description of the Pennant in his paper on the Fossil Flora of the 

 Bristol Coalfield.-' It might seem almost unnecessary to refer to the 

 existence of such a well-known formation as the Pennant, but for 

 the fact that in a recent scheme of the Carboniferous sequence in 

 Somersetshire the Pennant rock was wholly omitted. 



The interest now shifts from the almost continuous deposition of 

 the later Palaeozoics, in one great geosynclinal depression, to an. 

 entirely different class of phenomena. Nowhere, perhaps, are the 

 effects of the Post-Carboniferous interval better exhibited than in 

 those parts of the soi;th-west of England where Tertiary denudation 

 has removed the Mesozoic deposits. Here we perceive some of the 

 effects of the great foliations which terminated the Palaeozoic epoch 

 in this part of the world. The immense amount of marine denuda- 

 tion which characterizes this stage is particularly obvious in the 

 anticlinals, which were the first to suffer, as they came under the 

 planing action of the sea. 



Attention maj'^ be drawn to a peculiarity which has no doubt been 

 observed by many persons who have studied a map of the Bristol 

 and Somerset Coalfield. It will be seen that the strike of the Coal- 

 measures is widely different on either side of a line which may be 

 drawn through Mangotsfield to a point north of Bristol. The beds 

 north of this line have for the most part a meridional strike, nearly 

 parallel with the present Cotteswold escarpment ; south of this line 

 the strike is mainly east and west, though much curved in the 

 neighbourhood of Eadstock and the flanks of the Mendips. Of 

 course, this is only part of an extensive change in the direction 

 of flexure, much of which is still hidden under Mesozoic rocks. 

 Mr. Ussher, in the paper previously quoted, tells us that the line of 

 change of strike may be traced in the general mass of the Palaeozoic 

 rocks, from near Brecon in South Wales to the neighbourhood of 

 Frome, This means that within the Bristol district two distinct 

 systems of flexure must have impinged on each other in Post- 

 Carboniferous times. Have we not here, then, another instance of 

 extraordinary change within the limits of our area ? This time it is 

 not a mere change in the nature of a deposit, like that of the Old 

 Eed Sandstone into the Devonian, or of the Carboniferous Limestone 

 into the Culm-rock, but a change in the direction of the elevatory 



1 Proc. Cottes. Club, vol. vii (1878), p. 73. 



