§74 REPORT— 1898. 



Permian and newer Coal-Measures rest unconformably on overturned Silurian, Old 

 lied Sandstone, and older Coal-Measures. 



The folds of the Malvern and Abberley Hills are connected with those seen in 

 the Woolhope, May Hill, Usk, and Tortworth districts, and with those of the 

 Forest of Dean, South Wales and Bristol Coal-field ; and the author concludes that 

 these folds, together with those of other parts of the British Isles, belong to 

 the Great Hercynian system of mountains formed towards the close of the 

 Carboniferous period. 



5. 0)1 the Probable Source of the Upper Fehitic Lava of Snoicdon. 

 By J. R. Dakyns, M.A. 



Between Glaslyn and Bwlch Goch, as the lowest part of the ridge between 

 Crib Goch and the top of Crib y Ddysgl is called, a mass of felstone rises like a 

 wall through the beds of the calcareous ashy series. The trend of the dyke is 

 E.N.E. The best section is along the N.W. face, where the lelstone is clearly 

 seen standing as a wall against the truncated edges of the calcareous ashy beds. 

 The felstone shows lines of Jtow ■parallel to its side, and in some places is rudely 

 columnar, t/te axes of the prisms being perpendicular to the side of the dyke. It 

 is owing to this arrangement of the columns, and of the lines of How, that I con- 

 sider the rock to be a dyke. I call it a dyke because of the straightness of its 

 sides; but it is rather a boss than a dyke, as, while it is two hundred yards wide, 

 it is only about three or four hundred yards long. The rock is not like any of the 

 Lower Snowdonian felsites occurring in the immediate neighbourhood, but it is 

 decidedly like the upper felstone, which forms outliers on Crib Goch and Crih y 

 Ddysgl. It seems to me that we have here the source of the upper felsitic lava of 

 the Snowdon district. The boss is a plug of rock consolidated in and filling up 

 the orifice through which the upper lava flowed to the surface. 



6. On the Occurrence of Arenig Shales beneath the Carboniferous Rocks 

 at the Menai Bridge. By Edward Greenly. 



On the Carnarvonshire side of the Menai Straits, a little west of the suspension 

 'bridge, some dark shales have been found for a short distance along the shore, 

 unconformably underlying the carboniferous sandstones. They have yielded Arenig 

 Graptolites and Crustacea. On the Anglesey side, just opposite, pebbles of 

 similar shales, also yielding Llandrilo- Arenig fossils, have been found in some glacial 

 gravels. Taken in connection with other evidence it is inferred that these shales 

 in all prohability compose the floor of the Menai Straits east of the tubular bridge, 

 and that some additional light is thereby thrown upon the nature and physical 

 history of that hollow. 



7. On an Uplift of Boulders at Llandegfan, Menai Straits. 

 By Edward Greenly. 



A train of boulders of a massive grit, which occurs on the Anglesey shore of i 

 the Menai Straits at Garth Ferry, can be traced thence to the top of the hill at 

 Twr y Feliu, Llandegfan. The outcrops of the rock are almost entirely below the 

 50 feet contour, while the boulders are found in considerable numbers up to a 

 height of 330 to 340 feet. The direction of carry is W.S.W. to W., and the dis- 

 tance in a straight line from Garth Ferry to the top of the hill is about a mile. 



8. On the Comparative Dimensions of same Atoms. 

 By W. L. Addison. 



From the assumption that the attractive areas of the atoms behave as though 

 they possessed the form of the crystals, so that the crystal of an element may be 



