826 J. GEIKIE ON THE GLACIAL PHENOMENA 



In fig. 3 only the Interglacial beds appear ; but the coarse angu- 

 lar debris which underlies the laminated clay is probably the repre- 

 sentative of the Lower shelly Boulder-clay. 



In figs. 4 and 5 the Interglacial beds, which can usually be divided 

 into a lower clayey and an upper sandy series, are represented by 

 the beds marked b. At the Port of Ness they are exceedingly 

 coarse, rudely bedded, and charged with many large angular boulders. 

 In these respects they contrast somewhat strongly with their equi- 

 valents on the other side of the island. 



With the exception of a brick-clay that occurs in the Eye Penin- 

 sula, the deposits now described are the only shelly beds of glacial 

 age that I have met with in the Outer Hebrides. They are nowhere 

 seen in contact with the unfossiliferous bottom-till that forms the 

 main drift of Lewis ; and thus their relative position in the glacial 

 series can only be inferred from other evidence, to be stated in the 

 sequel. They do not seem to reach more than 100 feet above the 

 sea, but form a narrow belt of low ground that extends from the 

 Port of Ness across the island to the west coast between the mouth 

 of the Amhuinn Dhail and Sinntean. 



The Lower shelly Boulder-clay betrays no mark of aqueous origin, 

 but resembles in every respect a deposit that has been formed by the 

 direct action of glacier-ice. The broken shells that are scattered 

 through it show that the ice, underneath which it was rolled for- 

 ward, overflowed from what had previously been the sea-bottom ; 

 and the presence of many boulders of Cambrian rocks in the clay 

 indicates a movement from the east or south-east. 



The interglacial deposits point to a recession of the ice, during 

 which the Lower shelly Boulder-clay was much denuded. At this 

 time the sea overflowed the northern extremity of Lewis ; but the 

 extreme coarseness of the shingle beds at the Port of Ness would 

 seem to indicate that the submergence was very limited. The 

 laminated clay beds, however, were probably deposited in somewhat 

 deeper water, the overlying coarser beds pointing to the gradual 

 retreat of the sea or reelevation of the land. 



The Upper shelly Boulder-clay precisely resembles the Lower in its 

 origin. It points to the presence of glacier-ice that overflowed from 

 the bed of the Minch upon the low ground near the Butt, ploughing 

 into the preexisting drifts, confusing the bedding, and here and 

 there tumbling the strata up and incorporating them with its bottom- 

 moraine. 



Shelly Bride-clay. — At Garrabost, in the Eye Peninsula, there is 

 a dark greyish-blue clay, worked for brick-making. It appears to 

 be for the most part quite homogeneous, and shows little or no trace 

 of lamination. Here and there I picked out of it small fragments 

 of shells, none of which were recognizable. The relation of this 

 cla^ to the till of the neighbourhood was not apparent at the time 

 of my visit (1872) ; but I have since learned from the owner, Mr. 

 Henry Gaunter, some further details, which prove the clay to be of 

 interglacial age, as I had all along suspected. It was overlain, when 

 I saw it, by sand, like the interglacial silt beds near the Butt, and 



