On the Glaciated Summit of Allermuir, Pentlands. 307 



XXIX. On the Glaciated Summit of Allermuir, Pentlands. 

 By James Bennie, Esq., of the Geological Survey of 

 Scotland. 



(Read 18tli April 1883.) 



Some time during the spring of 1870 Dr Croll told me 

 that he intended going to some of the higher slopes of the 

 Pentlands to see how far np the ice markings of the glacial 

 period extended, and asked me to help him. I readily agreed, 

 and one bright morning we started for that purpose, duly 

 equipped with compass, hammer to take chips, spade to dig 

 for clay, and bag to carry the samples of each collected. 



We went through the fields to Swanston, going round the 

 farmhouse, up a defile, passing by the old village of Swanston, 

 and so on to the flanks of Caerketton. The way was pleasant, 

 and the suggestive talk of my companion made the walk 

 delightful and piquant. Among other things we discussed 

 the why and wherefore of our mission. 



Dr Croll said he had been trying lately to account for and 

 explain the condition of the boulder clay of Caithness, on the 

 theory that it was, like all the other boulder clays of Scotland, 

 the product of land ice. This theory he had applied to every 

 circumstance and characteristic of the Caithness boulder clay, 

 and found that it accounted for them more satisfactorily than 

 any other ; — nay, that the very exceptional one — the occur- 

 rence of fragments of marine shells throughout its entire 

 mass — was not against his theory, but in favour of it — indeed, 

 a main proof of its truth. 



Caithness, he said, being a low flat country — little more 

 than 30 feet above sea level — could not produce land ice of 

 its own to glaciate it, but that very circumstance made it 

 possible to be invaded and glaciated by land ice from other 

 regions. That ice he supposed to be the ice which flowed 

 outwards from the eastern slope of Scotland into the North 

 Sea, or rather the hollow now known as the German Ocean, 

 but which at that time could scarcely be called a sea, but 

 rather a mcv de glace filled with ice poured into it from the 

 Highlands on its eastern and western sides. That ice would 

 be certainly many hundreds of feet, perhaps some thousands 



