14 PROFESSOR P. F. KENDALL AND MR E. B. BAILEY 



gravels, on the other hand, which extend on to the latter from the hills, are everywhere 

 characterised by pebbles of Silurian grauwacke.* 



2. The excavation of the glacial drainage channels is responsible for another great 

 part of the material, especially, perhaps, that which litters the coastal plain. 



3. The ice sheet itself also no doubt directly supplied some proportion of the deposit. 

 As to the conditions regulating the accumulation of these sands and gravels, it 



seems certain that for the most part they formed either as the deposits of temporary 

 ice-dammed lakes or as gravel spreads extending between the ice and the hills and 

 reaching, along the coastal region, far out over the shelving bottom of the sea. 



It is difficult now to distinguish between these somewhat differently accumulated 

 deposits, and, in fact, one can only speak with confidence in special cases. It has been 

 found impossible to draw a line separating the gravel spread of the coastal plain into 

 two portions, according as it formed above or below the ancient high- water mark, or in 

 the inland sections to differentiate the material which accumulated in the temporary 

 lakes of the period. 



Not only were the original boundaries in the majority of such cases very blurred 

 and ill-defined in their nature, but also the deposits have since frequently taken on 

 outlines corresponding to a mature stage in erosion. We may illustrate this fact by 

 an example from the neighbourhood of Upper Keith ,t north-west of Fala. Several 

 interesting sections occur here, which render this the type area for the study of the 

 deposits, but their full description will be delayed till the section dealing with the 

 oscillatory nature of the retreat of the ice sheet. For the present it suffices that the 

 sections show a great mass of evenly bedded sands, with here and there a layer of 

 gravel or another of laminated clay or warp. The whole appears as the deposit laid 

 down in the tranquil waters of a great lake, but now so deeply eroded that it has taken 

 on the moundy form which one naturally associates with a sand district. Here and 

 there, indeed, flat stretches do exist which at first sight might be taken to mark an old 

 level of the lake waters ; but, as will appear later, these merely indicate the outcrop of a 

 more resistant bed of boulder clay which lies intercalated in the sands, and have there- 

 fore an entirely different significance. 



With this example in view it would be rash indeed to regard any of the " kame " 

 outlines, which are locally developed, as due to the preservation of original forms of 

 deposit. In fact, the most conspicuous example of kamiform ridges of gravel in this 

 district are afforded near Woodhall, south of Spott, where a section shows that the even 

 and almost horizontal bedding of the deposit bears no relation whatever to the external 

 form of the mounds, but is sharply truncated by the steep hill face. The interpretation 

 is obvious in this particular instance,! for the ridges are part of a gravel-spread which 

 formed between the hills and the ice sheet at a time when the glacial waters were being 



* Numerous exposures in the neighbourhood of Upper Keith, for instance, illustrate this point. 



t PI. IV. figs. 1 and 2. 



I We do not suggest for an instant that true kames of deposit do not exist in other districts. 



