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.