Yet even in those comparatively early days, some succession of glaciations was suspected. In 1845, Ramsay recognised three phases of ice-action in North Wales. In 1855, Morlot took in hand the work of charting the extent of several Swiss glaciations. At last the possibility of a subdivision of the boulder-clay was realised, and it was demonstrated by the researches of Sir A. Geikie[41] (1863). But such division of the boulder-clay leads directly to an inference of successive periods of deposition—and when the earlier opinion (whereby the boulder-clay was regarded as a submarine deposit) was partly abandoned in favour of its origin as a ‘ground-moraine,’ the plurality of glaciations was still more strongly supported. The work of Julien (Auvergne, 1869) and Professor James Geikie (1873) carries the story on to the year 1878 which is marked by a very memorable contribution from Professor Skertchley[42], by whom account was taken of the stratigraphical position of stone implements. The names of these pioneers (and that of Croll should be added to the list) may be fittingly recalled now that the names of later continental observers figure so largely. But the work of Professors Penck, Brückner, Boule and Obermaier, admirable as it is, may be regarded justly as an extension or amplification of pre-existing research.
A multiplicity of glaciations demonstrated whether by successive ‘end-moraines,’ or by a series of boulder-clays or ‘tills,’ implies intervening ‘inter-glacial’ epochs. To the earlier-recognised pre-glacial and post-glacial periods, one or more inter-glacial phases must therefore be added. Consequently the absence of evidence (indicative of Man's existence) from the boulder-clay need not exclude his presence in the inter-glacial deposits; and in fact the appearance of strongly-supported evidence that some implements of only Neolithic antiquity occur in inter-glacial surroundings, has been mentioned already (Chapter IV, Sturge, 1909). And thus, whether the series be one of grand oscillations constituting as many periods, or on the other hand a sequence of variations too slight to deserve distinctive terms, the fact of alternations prolonged over a considerable time seems to be established. Attempts to correlate various phases in the history of the animal and particularly of the human inhabitants of the affected area with these changes, still remained to be made.
Of such attempts, an early one, if not absolutely the earliest, stands to the credit of Dr Skertchley (1878). But in 1888 a much more definite advance was made by Professor Boule[43]. Still later came the suggestions of Professors Mortillet, Hoernes[44] (1903), Penck, Obermaier[45] (1909) and Tornqvist. And the employment of implements in evidence was found practicable by them. Ample compensation is thus provided for the lack of human bones, a deficiency almost as deplorable in 1911 as it was when Lyell called attention to it in 1863.
But the literature on this subject is so controversial and has attained such proportions, that the attempt to present current views will be limited to the discussion of the appended table (B). Here an endeavour has been made to submit the views expressed by the most competent observers of the day. The first point to which attention is directed consists in the manner in which the several glacial periods are distributed over the geological time-table. Boule claims one glaciation of Pliocene antiquity, followed by two Pleistocene glaciations. The remaining authors agree in ascribing all the glaciations to the Pleistocene period. Herein they follow the lead of Professor Penck, whose diagram of the oscillations in level of the snow-line in Central Europe is reproduced in Fig. 25. In the next place, the fact that Professor Penck's scheme was primarily intended to serve for the Swiss Alps must not be overlooked. That this system should leave traces everywhere else in Europe is not necessarily implied in accepting the scheme just mentioned.
In attempting to adjust the scale of glacial periods to that provided by the succession of implement-forms, it is suggested that a commencement should be made by considering the period designated Mousterian. If the position of the Mousterian period can be correlated with a definite subdivision of the Ice Age, then other periods will fall into line almost mechanically.
List of types of associated implements.
| Penck's scheme[1] | 1908 | 1908 | 1903 | 1908 | 1908 | 1878 |
| Boule[2] | Penck | Hoernes | Rutot | Sollas | Skertchley[3] | |
| Postglacial 4 = with Achen and other oscillations (Penck) | Magdalenian Solutréan[4] | Magdalenian | — | Neolithic period | ? | Neolithic period |
| Glacial IV 2nd Pleistocene(2) Glaciation of Boule. “Würmian” of Penck | Mousterian | Solutréan(4) | — | Lower Magdalenian Solutréan Aurignacian | ? | Hessle Boulder-clay |
| Interglacial 3 = Riss-Würm interval (Penck) | Mousterian (Obermaier) Chellean | Mousterian (warm phase) | Mousterian | Mousterian Upper Acheulean | Acheulean | Palaeoliths of the “modern-valley” type. Valley-gravels of present Ouse, Cam, etc. |
| Glacial III 1st Pleistocene Glaciation of Boule. “Rissian” of Penck | Chellean | Mousterian (cold phase) | — | Lower Acheulean Chellean | [Chalky Boulder-clay of Hoxne] | Purple Boulder-clay |
| Interglacial 2 = Mindel-Riss interval (Penck) | ? | Acheulean Obellean | Solutréan | Strépyan Mesvinian Mafflean | ? | Palaeoliths of “ancient-valley” type. ?Flood-gravels. Valleys do not correspond to modern rivers |
| Glacial II “Mindelian” of Penck | ? | ? | — | — | ? | Chalky Boulder-clay |
| Interglacial 1 = Günz-Mindel interval (Penck) | ? | ? | Mousterian Chellean | — | ? | Brandon beds with implements |
| Glacial I “Günzian” of Penck | ? | ? | — | — | ? | Cromer Till. Later than Forest-Bed |
[1] Penck postulates four glaciations, all “pleistocene.”
[2] Boule recognises two pleistocene glaciations (seemingly Nos. III and IV of Penck), and one pliocene glaciation. The latter is not indicated in the Table.