SECTIONAL TEANSACTIONR. — C. 357 



it is developed at various horizons and usually contains no 

 Ainmonites, but (.orrelatioii can be made by means of species 

 of Ostrea and Gryphen. In the numerous exposures near 

 Radstock many non-sequences can be located, and maps 

 showing the movement of intra-Liassic folds have been 

 prepared. 



9. Dr. J. K. Charles WORTH. — The Glaciation of the North- 

 West of Irelavd. 



The major part of the region investigated, including the 

 Donegal Highlands and the Sperrin jNIountains, was never 

 invaded by the Scottish ice as currently supposed, but the 

 Donegal mountains, in particular the Barnesmore Hills, 

 formed a most powerful centie of radiation, whence ice 

 streamed westwa.rds to the Atlantic and eastwards over the 

 Sperrin Mountains to Cookstown and beyond. In a south- 

 easterly direction the ice passed obliquely across the Clogher 

 Valley in Slieve Beagh to the Central Plain of Ireland, where 

 was located the ' central axis ' of Hull and Kilroe. This 

 axis of dispersal existed at no period of the glaciation. 



lO. Mr. L. Dudley Stamp. — On Cycles of Sedimentation in 

 the Eocene Strata of the Anglo-Franco-Belgian Basin. 



The Eocene deposits of the great Anglo-Franco-Belgian 

 Basin can be grouped naturally into a series of cycles of 

 sedimentation — the Montian, Landenian, Ypresian, Luetetian, 

 Ledian, and Bartonian. Each cycle commences with a marine 

 invasion and passes from marine to estuarine and continental 

 conditions. In England the changes are closely connected 

 with the gentle, intermittent uprise of the Weald. 



Friday, August 27. 



11. Dr. J. W. EvAxNS, F.E.S. — The Geological Structure of 

 North Devon. 



In early Permian times the Devonian and Carboniferous 

 were thrown by pressure from the south into overfolds, with 

 oveithrust faults. A subsequent relaxation of pressure 

 resulted in a slip hack on the same fault-planes. There were 

 also oblique tear-faults striking between north and west. 

 A mountain region then sloped southward from the Welsh 

 Coast to Mid-Devon and much material was transported in 

 that direction. In the Triassio period, however, the 

 Palteozoic had, as a whole, its present contours, including 

 the great Cllastonbuiy and Bristol Channel depression 

 descending to the west, and its subsidiary valleys still partly 

 filled with Mesozoic deposits. In Tertiary times there was 

 renewed pressure from the south. This met with less 

 lesistance in the west, and there was consequently a relatively 

 forward and downward movement on that side along the old 

 tear-faults and possibly new fractures with the same general 

 direction. In Pliocene times the land was more submerged 

 than now and the subsequent emergence seems to have con- 

 tinued in most places till a comparatively recent date. 



12. Prof. W. L. Bragg. — Crystal Structure. 



The investigation into crystal stnicture, which has been 

 made feasible by the discovery of the diffraction of X-rays 

 by crystals, has led to a determination of the precise positions 

 of the atoms in a number of the simplex ciystalline forms. 

 Recent theories of atomic structure, such as those put 

 forward by Bom and Lande, Debye, Lewis, and Langmuir, 



