On the Volcanic Rocks of North-eastern Fife. 11 



the north, where the existence of an ice-sheet has been strongly 

 advocated. Anglesey is considered by Sir A. Eamsay to have 

 received its configuration by the action of an ice-sheet from the 

 north ; but its physical features appear to be due rather to its geo- 

 logical structure, and to have existed in more or less their present 

 form iu pre-glacial times. 



The arrangement of drifts in this district presents an analogy with 

 that of the Norfolk drifts, and probably results from a similar 

 sequence of events. 



The marine drifts, from their great variability, seem to have been 

 distributed, and the striations produced by floating ice, driven by 

 tidal or oceanic currents, during the time of submergence. During 

 this time Snowdon and the surrounding hills must have stood well 

 above water, forming an island-group, and by such a group the pre- 

 vailing currents from the north would be deflected to the south- 

 west over Anglesey on the one side, and to the south-east over the 

 plains of Cheshire and Shropshire on the other, while within the 

 limits of the group a local circulation might be maintained. 



June 9.— Prof. J. W. Judd, F.R.S., President, in the Chair. 



The following communications were read : — 



1. "On the Volcanic Rocks of North-eastern Fife." By James 

 Durham, Esq., F.G.S., with an Appendix by the President. 



After describing the general distribution of the volcanic rocks of 

 Old Red-Sandstone and Carboniferous age in the counties of Forfar 

 and Fife, the author called attention to a fine section exhibited 

 where the Ochil Hills terminate along the southern shore of the 

 Firth of Tay. In immediate proximity to the Tay Bridge, a series 

 of the later volcanic rocks, consisting of felstones, breccias, and 

 ashy sandstones, are found let down by faults in the midst of the 

 older porphyrites (altered andesites) which cover so large an area 

 in the district. The breccias contain enormous numbers of blocks 

 of a red dacite (quartz-andesite), and enclosed in this rock angular 

 fragments of a glassy rock, resembling a " pitchstone-porphyry," are 

 found, everywhere, however, more or less converted into a white 

 decomposition-product. The youngest igneous rocks of the district 

 are the bosses and dykes of melaphyre (altered basalt and dolerite) 

 which have been often so far removed by weathering as to leave 

 open fissures. 



In the Appendix three very interesting rocks were described in 

 detail. The rock of the JNorthfield Quarry, which is shown to be 

 an augite-andesite, has a large quantity of a glassy base with 

 felted microlites, and contains large porphyrinic crystals of a colour- 

 less augite. The rock of the Causewayhead Quarries is described 

 as an enstatite-andesite ; it has but little glassy base, being made 

 up of lath-shaped felspar crystals (andesine), with prismatic crystals 

 and grains of a slightly ferriferous enstatite ; there are no por- 

 phyrinic crystals, but the enstatite individuals are sometimes 

 curiously aggregated. The red porphyritic rock from the breccias 

 near the Tay Bridge was shown to be a mica-dacite, and the glassy 



