150 Geological Society: — 



support of his contention that the main snow-fall in Glacial times 

 would be on the western mountains. He gives reasons for supposing 

 that, previously to the formation of the lake, the valleys of the 

 Lochaber lakes were occupied by ice, and that the period of the 

 formation of the lakes was that of the decay of the last Ice-sheet. 



He supports the correctness of the mapping of the terraces by the 

 officers of the Ordnance Survey, and shows how the absence of the 

 two upper terraces in Glen Spean and of the highest terrace in Glen 

 Glaster simplifies the explanation of the formation of the lakes by 

 ice-barriers. 



The alluvium of Bohuntine is considered to be the gravel and 

 mud that fell into the lake from the front of the ice when ifc stood 

 at the mouth of Glen Roy during the formation of the two upper 

 lines. 



During the last stage of the lake, the ice in the valley of the 

 Caledonian Canal is believed to have constituted the m?in barrier, 

 whilst the Corry N'Eoin glacier played only a subordinate part. 



The author suggests the possibility of a debacle during the drop 

 of water from the level of the highest to that of the middle terrace ; 

 and in support of this calls attention to the breaking down of the 

 moraines of the Treig glacier at the mouth of the Rough Burn. He 

 believes that when the water dropped to the level of the lowest 

 terrace, it drained away quietly, at any rate until it receded from 

 Upper Glen Roy. 



In discussing Nicol's objections, he maintains that notches would 

 not be cut at the level of the cols, and observes that the discrepancy 

 between the heights of the terraces and those of the cols has pro- 

 bably been increased by the growth of peat over most of the ground 

 about the watersheds. 



The horizontality of the terraces is stated to be a fact, and cases 

 are given where waterworn pebbles are found in connexion with the 

 " roads," these being especially noticeable in places where the south- 

 west winds would fully exert their influence, and the structure of 

 the terraces is considered to be such as would be produced at the 

 margins of ice-dammed lakes. Further information is supplied 

 concerning the distribution of the boulders of Glen Spean syenite. 

 These are found on the north side of the Spean Valley at the 

 height of 2000 feet above the sea and 1400 feet above the river, 

 and fragments of the syenite have been carried towards the north- 

 east, north, and north-west. 



In an Appendix, the author discusses Prof. Prestwich's remarks 

 on the deltas, and his theory of the formation of the terraces. 



November 25.— Sir Archibald Geikie, D.Sc, LL.D., F.R.S., 

 President, in the Chair. 



The following communications were read : — 

 1. " On the Os pubis of Polacantlius Foxi." By Prof. H. G. Seeley, 

 F.R.S., P.G.S. 



