3 86 



PREHISTORIC EUROPE. 



of the Tay and the Earn, a short description of that region will 

 serve to show the general mode of their occurrence, and the 

 nature of the deposits with which they are usually associated. 



The accompanying illustration brings into one view the more 

 prominent features of the late glacial and postglacial accumu- 

 lations as these are developed in the valleys of the Tay and the 



Fig. 11. — Diagrammatic section across Carse of Gowrie. 1, Till ; 2, Late glacial 

 clays, etc. ; 3, River -shingle, gravel, etc. ; 4, Peat and forest-bed; 5, Carse-clay ; 

 6, Recent alluvia. 



Earn. Eesting upon the strata of Old Eed Sandstone age comes 

 first a mass of tough reddish boulder-clay (1), overlying which 

 we find a considerable thickness of gravel, sand, and brick-clays 

 (2). Next in ascending order are beds of gravel, sand, and silt 

 (3), resting upon an eroded surface of the underlying deposits. 

 Above these younger sand- and gravel-beds appears a stratum of 

 peat (4), surmounted by a widespread accumulation of silt and 

 clay (5). To a still later period belong the alluvial deposits 

 (6). Let us now glance at the more salient characteristics of 

 each of these divisions in succession, and see what they have 

 to tell us of physical and climatic changes. 



1. The Till or Boulder-clay need not detain us. It is a 

 highly typical glacial accumulation, and represents the bottom- 

 moraine of the last ice-sheet which overflowed all the low grounds 

 of Scotland. 



2. Eesting upon the denuded surface of this boulder-clay 

 comes a series of aqueous deposits, consisting in some places of 

 shingle and boulders, or of gravel and sand, and in other places 

 of fine brick-clays. The upper surface of these deposits is com- 

 paratively flat, and reaches 100 feet above the sea-level. They 

 appear at one time to have filled up to that level the whole of 

 the lower reaches of the valleys of the Tay and the Earn, and 

 their denuded remains still form a more or less well-marked 



