472 Reports & Proceedings— British Association. 



at various horizons, and usually contains no Ammonites, but correlation 

 can be made by means of species of O-^trea and Grj/j^hea. In the numerous 

 exposures near Radstock many non-sequences can be located, and maps 

 showing the movement of intra-I.iassic folds have been prepared. 



9. Dr. J. K. Charlesworth : The Glaciation of the North- 

 West of Ireland. 



The major part of the region investigated, including the Donegal 

 Highlands and the Sperrin Mountains, was never invaded by the Scottish 

 ice as currently supposed, but the Donegal mountains, in particular the 

 Barnesmore Hills, formed a most powerful centre of radiation, whence 

 ice streamed westwards to the Atlantic and eastwards over the Sperrin 

 Mountains to Oookstown and beyond. Jn 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. 



10. Mr. L. Dudley Stamp : On Cycles of Sedimentation in the 

 Eocene Strata of the Anglo-French-Belgian Basin. 



The Eocene deposits of the great Anglo Franco-Belgian Basin can be 

 grouped naturallj^ into a series of cycles of sedimentation— the Montian,, 

 Landenian, Ypresian, Lutetian, Ledian, and Bartunian. Each cycle 

 commences with a marine invasion and passes from marine to estua.rine 

 and continental conditions. In England the changes are closely connected 

 with the gentle, intermittent uprise of the Weald. 



11. Dr. J. W. Evans, F.R.S. : The Geological Structure of 

 North Devon. 



In early Permian times the Devonian and Carboniferous were thrown 

 by pressure from the south into overt olds, with overthrust faults. 

 A subsequent relaxation of pressure resulted in a slip back 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 Triassic period, however, the Palaeozoic had, as a whole, its present 

 contours, including the great Glastonbury and Bristol Channel depression 

 descending to the west, and its subsidiary valleys still partly filled with 

 Mesozoic dej)osits. In Tertiary times there was renewed pressure from 

 the south. This met with less resistance in the west, and there was 

 consequently a relativelj' forward and downward movement on that side 

 along the old tear-faults and possibly new fractures with the same general 

 dii'ection. In Pliocene times the land was more submerged than now, 

 and the subsequent emergence seems to have continued in most places till 

 a comparatively recent date. 



12. Professor W. L. Bragg : Crystal Structure. 



The investigation into crystal structure, 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 

 simpler crystalline forms. Recent theories of atomic structure such as 

 those put forward by Bom and Lande, Debye, Lewis, and Langmuir, are 

 largely based on the arrangement of the atoms in crystalline solids, 

 since this arrangement affords an insight into the nature of the forces 

 acting between the atoms. In such compounds as sodium chloride, it 

 is probable that the atoms exist as ions of sodium and chlorine, and that 

 the crystal is held together by the electrostatic attractions of these ions,, 

 thus accounting for the fact that there is no grouping of the atoms into 

 molecules in the solid. In other compounds, such as those of two 

 electronegative elements, the molecular arrangement persists in the solid 

 state and the chemical combination appears to be v)f a different type 



