O. W. Bulman — Glacial Geology. 347 



Prof. Geilde agrees with M. Morlot as to the relative severity of 

 the two glacial epochs : 



" The glaciers of the second period, although of very much larger 

 dimensions than their puny descendants of to-day, yet were them- 

 selves but pigmies as compared to the gigantic ice-flows of the first 

 period." 



But surely it would be difficult, or even impossible, to distinguish 

 between glacial deposits formed at two distinct epochs of such 

 character separated by a mild interval, but with no distinct memorials 

 of the latter, and a series of deposits formed by ice-sheets and 

 glaciers continuously or intermittently retiring. If the ice, after 

 gradually retiring to a certain point, made a prolonged pause before 

 finally shrinking to its present limits, we might expect to find two 

 apparently distinct sets of deposits such as those described, and one 

 of which indicated a much more limited extent of ice. In fact, all 

 the phenomena of these Swiss beds here mentioned are not only 

 possible on the hypothesis of an oscillating and intermittently 

 retiring body of ice, but are exactly such as we should expect on 

 this view. 



And Prof. Prestwich does not consider the evidence of these beds 

 — nor indeed the evidence for interglacial periods generally — as 

 conclusive. 



" It is asserted," he writes, " that in Europe there were interglacial 

 periods during which the ice disappeared from the surface for great 

 lengths of time. But either the evidence is insufficient or it points 

 to slight temporary effects, except in one case, which is of more 

 importance, and on which the greatest stress is laid, namely, that of 

 Diirnten in Switzerland. There beds of lignite with mammalian 

 remains are intercalated between two glacial deposits. Admitting 

 the fact that the lignite rests on beds of undoubted glacial (ground- 

 moraine) origin, and that the trees grew on the spot where their 

 stumps and remains are found, it by no means follows, as contended, 

 that because these trees are all of species now living in Switzerland, 

 the temperature was that of Switzerland of the present day. Pinus 

 sylvestris, Abies exceJsa, the Yew, the Birch, and the Oak flourish 

 equally in Sweden and far north in Siberia. On the other hand, 

 there is one species of Finns (P. montana) which is spread over the 

 mountain country up to heights of 7000 feet, and is rare in the low 

 lands ; while one of the Mosses is closely allied to a species now 

 growing on the hills of Lapland. The few species of Mammalia 

 have a distinctly northern facies. Elephas primigenius, E. antiquus, 

 Ursus spelcsus, as also Cervus elaphus, and Bos primigenius, are 

 commonly associated with the Reindeer, Musk, etc., and other 

 Arctic animals of the cold post-glacial times. 



Is the return, therefore, of the retreating glacier, supposing the 

 boulder-gravel above the lignites of Diirnten to be due to direct 

 ice-action, to be ascribed to anything more than a comparatively 

 slight temporary change of climate, like those that now for a 

 succession of seasons cause, from time to time, a temporary advance 

 of the glaciers, only more marked? We must allow, of course, 



