Reports and Proceedings — Geological Society of London. 39 



and Mark. The depth of strata likely to cover the PalEeozoic floor 

 at these places might be expected to vary from four or five hundred 

 to a thousand feet, but it is improbable that it would anywhere 

 exceed a thousand feet. 



In connection with the disturbances to wbicb the Mendip area has 

 been subjected, Mr. Ussher introduces a diagram to explain by 

 means of a thrust-plane the occurrence of the little masses of 

 Carboniferous Limestone that overlie the Coal-measures at Vobster 

 on the northern side of the Mendip anticline. H. B. W. 



lasiPOE-TS .A^isTZD :PI^ooEEI^I2^^<3-s. 



Geological Society of London. 



I.— Nov. 11, 1S91.— Sir Archibald Geikie, D.Sc, LL.D., F.R.S., 

 President, in the Chair. — The following communications were read : 



1, " On Dncrytlierium ovinum from the Isle of Wight and Quercy." 

 By R. Lydekker, Esq., B.A., F.G.S. 



The author described a cranium and mandible of Dacrytherium 

 Cayluxi from the Quercy Phosphorites, which proved the identity of 

 this form with the Dicliohune ovina of Owen from the Oligocene 

 of the Isle of Wight. The species should thus be known as Dacry- 

 therium ovinum. It was shown that the mandible referred by Filhol 

 to D. Cayluxi belongs to another animal. 



2. " Supplementary Eemarks on Glen Roy." By T. F. Jamieson, 

 Esq., F.G.S. 



The author discusses the conditions that preceded the formation 

 of the Glen Roy Lake, and appeals to a rain-inap of Scotland in 

 support of his contention that the main snowfall 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 

 ofiScers 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 it 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 Cale- 

 donian canal is believed to have constituted the main 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 



