TRANSACTIONS OF SECTION C. 659 



so-called Ma^nesian Limestone at Glevedon, against the Carboniferous Limestone, 

 causing rolls and fractures for the space of some 500 feet, when the latter formation 

 appears agiin, but now with the Dolomitic Conglomerate, everywhere resting hori- 

 zontally on its upturned and denuded edges. (3) The cropping up of the ' Bryozoa ' 

 bed just before the last tunnel, giving a definite horizon for the correlation of this 

 section with that at the Avon gorge. (4) The appearance at the base of the section 

 of the Old Red Conglomerate with the coarse Dolomitic Conglomerate, containing 

 pebbles of white quartz, Old Red Sandstone and Limestone, resting on its edges and 

 with dithculty to be distinguished from the latter, (o) The reappearance at the 

 end of the cutting of the same fine-grained yellow limestones divided by bands of 

 shale and clay lying horizontally on the coarse Conglomerate beneath. 



6. The Norihern Section, of the Bristol Coal-field. 

 Bij Haxdei. Cossham, M.F., F.G.8. 



After some general remarks on the character of the Bristol Coal-field, and its 

 more complicated geological features, the author referred to the opinions of the 

 principal geologists who have described the district, and recalled attention to his 

 paper on a mistake in the geological maps of this Coal-field (read at the Bath 

 meeting of the British Association in 1864). 



He then drew attention to certain remarkable faults found in the Bristol Coal- 

 field, with explanations of the same ; and observed that they furnished illustra- 

 tions of lateral pressure rather than of vertical movement. 



He gave some account of the upheaval of the Mendip Hills, Broadfield Down, 

 &c., subsequent to the formation of the Coal-field; alluding to the rent in the 

 Palaeozoic strata which forms the Severn valley, and to the severance of the Coal- 

 fields of South "Wales, Dean Forest and Bristol. A remarkable discovery was 

 made by him, in 1884, of a great overthrust fault, the effect of which has been to 

 double the known coal resources on the western side of the Bristol Coal-field. His 

 observations threw some light on the complicated geological section of the Avon 

 gorge, and on the future of the Bristol coal supply. 



7. Some Points of Interest in the Geology of Somerset. 

 By W. A. E. UssHER, F.G.S. 



[Communicated by permission of the Director-General of the Geological Survey.] 



Three subjects were put forward as worthy of attention, and demanding a solu- 

 tion. 



First. The position of the Carboniferous Limestone patches in the Coal- Measure 

 area at Vobster and Luckington. 



Secondly. The borderland between the Devonian and Culm Measures and the 

 rocks of Old Red Sandstone and Carboniferous (proper) type. 



Thirdly. The relations of the Lower Devonian beds in West Somerset. 



In the first place, he suggested a thrust-fault through the Mendip axis carryin"- 

 its upper portion northward so that the upward continuation of the Limestone on 

 the north side of the Mendips should be shifted to the position indicated by the 

 Vobster patches, the relations of these patches to the Coal Measures beneath and 

 around being subsequently affected bv step faults. This alternative hypothesis 

 seemed to him more simple than Mr. H. B. Woodward's faulted anticlinal curves 

 and was merely put forward as a tentative hypothesis. 



In the second place the author deprecated absolute correlations of divisions of 

 Devonian and Carboniferous beds, whilst accepting the philo.'sophical aspects of the 

 general correlations of the late Professor Jukes and of Professor Hull. He con- 

 sidered that the area in which both types occurred side by side deserved primary 

 attention. The relative position of the Cannington Park (Carboniferous) Lime- 

 stone to the Middle Devonian rocks of the Quantocks and the Cannington and other 

 inliers, supposed to be Middle Devonian, was given, as also the position of the 



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