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IX. — On the Glacial Succession in Europe. By Professor James Geikie, 

 D.C.L., LL.D., F.K.S., &c. (With a Map.) 



(Read 16th May 1892.) 



For many years geologists have recognised the occurrence of at least two boulder- 

 clays in the British Islands and the corresponding latitudes of the Continent. It is no 

 longer doubted that these are the products of two separate and distinct glacial epochs. 

 This has been demonstrated by the appearance of intercalated deposits of terrestrial, 

 freshwater, or, as the case may be, marine origin. Such interglacial accumulations 

 have been met with again and again in Britain, and they have likewise been detected at 

 many places on the Continent, between the border of the North Sea and the heart of 

 Kussia. Their organic contents indicate in some cases cold climatic conditions ; in others, 

 they imply a climate not less temperate or even more genial than that which now 

 obtains in the regions where they occur. Nor are such interglacial beds confined to 

 northern and north-western Europe. In the Alpine Lands of the central and southern 

 regions of our Continent they are equally well developed. Impressed by the growing 

 strength of the evidence, it is no wonder that geologists, after a season of doubt, should 

 at last agree in the conclusion that the glacial conditions of the Pleistocene period were 

 interrupted by at least one protracted interglacial epoch. Not a few observers go 

 further, and maintain that the evidence indicates more than this. They hold that three 

 or even more glacial epochs supervened in Pleistocene times. This is the conclusion I 

 reached many years ago, and I now purpose reviewing the evidence which has accumu- 

 lated since then, in order to show how far it goes to support that conclusion. 



In our islands we have, as already remarked, two boulder-clays, of which the lower 

 or oldest has the widest extension southwards, for it has been traced as far as the valley 

 of the Thames. The upper boulder-clay, on the other hand, does not extend south of 

 the Midlands of England. In the north of England, and throughout Scotland and the 

 major portion of Ireland, it is this upper boulder-clay which usually shows at the surface. 

 > The two clays, however, frequently occur together, and are exposed again and again in 

 deep artificial and natural sections, as in pits, railway-cuttings, quarries, river-banks, and 

 sea-clifls. Sometimes the upper rests directly upon the lower ; at other times they are 

 separated by alluvial and peaty accumulations or by marine deposits. The wider 

 distribution of the lower till, the direction of transport of its included erratics, and the 

 trend of the underlying roches moutonnees and rock-striae, clearly show that the earlier 

 mer de glace covered a wider area than its successor, and was confluent on the floor of 

 the North Sea with the Scandinavian ice-sheet. It was during the formation of the 

 lower till, in short, that glaciation in these islands attained its maximum development. 



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