GLACIAL SUCCESSION IN EUROPE. 135 



separated from that of the preceding ice-sheet by a prolonged interval of interglacial 

 conditions. One link in the chain of evidence, however, was wanting : I could not point 

 to the occurrence of interglacial deposits underneath the great valley-moraines. But 

 these, as we have seen, form a well-marked horizon on the Continent, and we cannot 

 doubt that a similar interglacial stage obtained in these islands. We may feel confident, 

 in fact, that genial climatic conditions supervened on the dissolution of the last great 

 mer de glace in Britain, and that the subsequent development of extensive snow-fields 

 and glaciers in our mountain regions was contemporaneous with the appearance of the 

 last great Baltic glacier. 



We need not be surprised that interglacial beds should be well developed underneath 

 the bottom-moraine of that great glacier, while they have not yet been recognised below 

 the corresponding morainic accumulations of our Highlands and Uplands. The conditions 

 in the low grounds of the Baltic coast-lands favoured their preservation, for the ice in 

 those regions formed a broad mer de glace, under the peripheral areas of which sub- 

 glacial erosion was necessarily at a minimum and accumulation at a maximum. In our 

 mountain valleys, however, the very opposite was the case. The conditions obtaining 

 there were not at all comparable to those that characterised the low grounds of Northern 

 Germany, &c, but were quite analogous to those of Norway, where, as in our own 

 mountain regions, interglacial beds are similarly wanting. It is quite possible, however, 

 that patches of such deposits may yet be met with underneath our younger moraines, 

 and they ought certainly to be looked for. But whether they occur or not in our 

 mountain valleys, it is certain that some of the older alluvia of our lowlands must belong 

 to this horizon. Hitherto all alluvial beds that overlie our upper boulder-clay have been 

 classified as postglacial ; but since we have ascertained that our latest mer de glace was 

 succeeded by genial interglacial conditions, we may be sure that records of that temperate 

 epoch will yet be recognised in such lowland tracts as were never reached by the glaciers 

 of the succeeding cold epoch. Hence, I believe that some of our so-called " postglacial " 

 alluvia will eventually be assigned to an interglacial horizon. Amongst these may be 

 cited the old peat and freshwater beds that rest upon the upper boulder-clay at Hailes 

 Quarry, near Edinburgh. To the same horizon, in all probability, belong the clays, with 

 Megaceros, &c, which occur so frequently underneath the peat-bogs of Ireland. An 

 interesting account of these was given some years ago by Mr Williams,* who, as a 

 collector of Megaceros remains, had the best opportunity of ascertaining the nature of 

 the deposits in which these occur. He gives a section of Ballybetagh Bog, nine miles 

 south-east of Dublin, which is as follows : — 



6. Peat. 



5. Greyish clay. 



4. Brownish clay, with remains of Megaceros. 



3. Yellowish clay, largely composed of vegetable matter. 



2. Fine tenacious clay, without stones. 



1. Boulder-clay. 



* Geol. Mag., 1881, p. 354. 

 VOL. XXXVII. PART I. (NO. 9). Y 



