as President, to the Geological Section. 461 



The Carboniferous Limestone of the Bristol area has attracted the 

 attention of so many distinguished geologists that its palaeontology 

 and general features are tolerably familiar. Of late years we owe 

 some interesting petrographic details to Mr. Wethered. The varying 

 thickness of the Carboniferous Limestone and also of the Millstone 

 Grit in this part of England is noteworthy. If we follow the 

 Carboniferous Limestone in a south-westerly direction, across the 

 mysterious Bridgewater flats, a change is already noted in the case 

 of the Cannington Park limestone, which was the subject of so much 

 discussion in former years. Referring to this, Mr. Handel Cossham ^ 

 was so sanguine as to believe that .its identification with the 

 Carboniferous Limestone would have the effect of extending the 

 Bristol Coalfield thirteen miles south of the Mendips. However 

 this may be, all further traces of Carboniferous rocks fail at this 

 point. After crossing the Yale of Taunton, when next we meet 

 with them in the Bampton district, the Culm-measure type, with 

 its peculiar basal limestones, is already in full force. 



In the new " Index Map " the Culm-measures are placed at the 

 base of the Carboniferous series — below the Carboniferous Limestone. 

 It is no part of my purpose to attempt any precise correlation, but 

 I would point out the somewhat singular circumstance that the 

 change to Culm rock occurs only a few miles to the south-west of 

 the line where, in the previous system, we have already seen that 

 the Old Red Sandstone changes into the Devonian. This curious 

 coincidence may be wholly accidental, or it may be the result of 

 some physical feature now concealed by overlying formations. 



Since 1895 a new light has been thrown on the lower Culm- 

 measures by the discovery of a well-marked horizon of Radiolariau 

 rocks. One result of the important paper of Messrs. Hinde and Fox 

 has been to alter materially our views as to the physical conditions 

 accompanying the deposition of a portion of the Culm-measures. 

 The pala3ontology leads the authors to conclude ^ that " the Lower 

 Posidonomya- and Waddon Barton Beds are the representatives and 

 equivalents of the Carboniferous Limestone in other portions of the 

 British Isles ; not, however, in the at present generally understood 

 sense that they are a shallow-water facies of the presumed deeper- 

 water Carboniferous Limestones, but altogether the reverse, that 

 they are the deep-water representatives of the shallower-forn^ed 



calcareous deposits to the north of them The picture that 



we [Messrs. Hinde and Fox] can now draw of this period is that 

 while the massive deposits of the Carboniferous Limestone — formed 

 of the skeletons of calcareous organisms — were in the process of 

 growth in the seas to the north [i.e. in the Mendip area and 

 elsewhere] there existed to the south-west a deeper ocean in which 

 siliceous organisms predominated and formed these siliceous radio- 

 larian rocks." 



This is probably a correct view of the case, but one cannot help 

 wondering that the ocean currents and other causes did not effect 



1 Proc. Cottes. Club, vol. yiii (1881-2), p. 20 et seq. 



2 Quart. Joui-n. Geol. Soc, vol. li (1895), p. 662. 



