534 TRANSACTIONS OF SECTION C. 



I need hardly remind you that, according to CroU, a sufficient explanation of 

 the Glacial Period could be found in certain astronomical conditions, which ■were 

 shown by his calculations to have recurred at definite intervals, and were supposed 

 to have produced repeated alternations of cold and warm climate at the opposite 

 hemispheres durinf^ the course of the period. It is not my purpose to discuss this 

 or any other theory regarding the cause of the Great Ice Age, but only to direct 

 your attention to the influence of Croli's views upon the work of observation. If 

 the theory could have been sustained, it would have given into the hands of the 

 geologist a first instalment of that absolute measure of geological time which he 

 60 ardently desires ; and with this allurement it is no wonder that the theory was 

 welcomed and hopefully put to the test. Foremost among its exponents was 

 Professor James Geikie ; and we must all recognise that its main importance to 

 the field-geologist arose from his powerful support and masterly arrangement of 

 the evidence favourable to the hypothesis. 



It is not surprising that, amid the complicated mass of facts confronting us in 

 the glacial deposits and among the voluminous literature wherein these facts are 

 more or less skilfully enwrapped, there should have been found some material to 

 support the idea of a recurrent succession of glacial and interglacial stages. But 

 the glamour of the astronomical hypothesis has waned, and it is recognised that 

 there are flaws in the physical aspect of the theory and in its geological application 

 that render it untrustworthy. I think, therefore, that the time has come when 

 we should reconsider the matter in critical mood, uninfluenced by the early glow 

 of the theory, after the wise example of that ancient people who debated all 

 matters of import in two opposite frames of mind. 



On the present occasion it would be impossible adequately to discuss Ihe whole 

 subject, and I propose to deal principally with my own experience in attempting 

 to apply the Interglacial hypothesis to my field-work. I hope also to be able 

 briefly to review the evidence from other parts of our islands in the light of this 

 experience. 



And here I may remind you of the important part which this Section of the 

 British Association has taken in the study of the subject by organising Committees 

 of Itesearch, provided with funds for carrying out excavation and other necessary 

 work. During the twenty-five years since we last met at York 1 find that, includ- 

 ing the work in certain bone-caves, there have been fourteen such committees ; 

 and in many cases their operations have extended over several years, so that over 

 thirty separate reports have been published in the Annual Reports of the Associat ion.' 

 The precise information embodied in these reports is of high scientific value, and I 

 am sure that these residts are very creditable to the Section. 



Classification of the Drifts. 



I have mentioned the influence of Professor J. Geikie in the establishment of 

 the Interglacial hypothesis; and before proceeding further it is necessary that we 

 should recapitulate the scheme of classification which he has proposed for the drifts 

 on the basis of this hypothesis. This elaborate scheme has been built up by a 

 skilful combination of evidence gleaned from various parts of Europe, and repre- 

 sents the hypothesis in its extreme form. Stated in downward succession it stands, 

 in its latest development,* as follows : — 



' Y'vi., Reports on ' Raygill Fissure ' (1883-1886) ; ' Manure Gravels of Wexford,' &c. 

 (1887-1890); ' Welsh Caves' (1886 and 1898); ' Sewerby Raised Beach ' (1888-1890); 

 'Elbolton Cave' (1891-1894); ' Scottish Marine Drifts' (1893-1896) ;' Calf Hole, 

 Skiplon' (1894); 'Hoxne Plant Beds' (1896); 'Irish Elk in the Isle of Man' (1897- 

 1900); 'Pleistocene Beds near Toronto ' (1898-1900); 'Moel Tryfaen Drift' (1898) ; 

 'Uphill Cave' (1899-1901); 'Irish Caves' (1901-1904); ' Kirmington and other 

 Fossiliferous Drifts ' (1903-1905). During the same period there have also been 

 twenty- three reports of the ' Erratic Blocks ' Committee, which bear indirectly upon 

 the problem. 



* ' The Classitication of European Glacial Deposits.' Journ, <?<?<>?. (Chicago), vol, iii, 

 (1895), pp. 241-269. 



