SECTIONAL TRANSACTIONS.— H. 383 



Acheul, distinguishing many more intermediate stages. In the flake industry we 

 ha\e the types known as Levallois and Le Moustier and perhaps others. 



Collections from many sites exhibit most if not all the stages of the core industry, 

 all apparently unrolled, and the deposit can only be dated by the most developed 

 types found, since the others appear to be rough or possibly unfinished tools ; much 

 the same may be said for the flake industry. Moreover, the latter industry was 

 present long before the former went out of use, though it may, and probably did, 

 continue later, at any rate in North-west Europe. Thus, the simple succession, 

 Early Chelles, Chelles, Evolved Chelles, St. Acheul and Le Moustier no longer holds 

 good. 



Further than this, implements of St. Acheul type have been found in plateau 

 gravels, at any rate as high as 150 feet above river level, and I believe higher. The 

 circumstances under which these have been found suggest that they may have been 

 dropped on the surface of these gravels long after the latter were deposited, and 

 subsequently covered over by rearrangement of the surface. We cannot, I think, 

 be absolutely sure that the same process has not occurred in lower gravek, like the 

 Boyn Hill terrace at Maidenhead, 80 feet above river level. The same criticism 

 applied, though perhaps in a lesser degree, to the various types of the flake industry. 



It is true that there may be difficulties in using for our purpose sea-terraces, not 

 so much because of differential movements, which have been hardly sufficient to 

 disturb our conclusions, at any rate south of the Humber, but owing to the scarcity 

 of the deposits. River-terraces are, however, plentiful, especially in the Thames basin 

 and elsewhere in the South and East of England. 



Speaking as an amateur, with a slight experience only of the Thames basin, I 

 would suggest that the problem would be advanced if the whole of this basin, and 

 others in neighbouring areas to the North and South of it, were examined with the 

 detail and accuracy employed by Overy and Sandford in deaUng with the Upper 

 Thames. We need, I would suggest, a number of accurate sections across the valleys 

 of the Thames and its tributaries, showing in the case of each terrace and plateau 

 gravel the height of the base and the highest level reached, given in terms of height 

 above the present summer level of the river at that spot. If such sections, at no 

 great intervals, were made for the Thames basin, the Hampshire basin and the basin 

 of the Wash, these could probably be correlated with accuracy. The East Anglian 

 gravels are in close connection with the boulder clays, as are some of the Thames 

 gravels in Hertfordshire and Essex. It would thus be possible to correlate the 

 terraces with the different boulder clays, and thus with the northern ice-sheets. 



Again, it should be possible to equate our terraces, not only with those of the 

 Somme, but with those of the Rhine, and by means of the latter river with the Alpine 

 glaciations. It is even possible that the desired correlation could be obtained from 

 evidence in the Rhine basin alone, since its source is in the midst of the Alpine region, 

 while on its passage through Holland it cuts across a moraine of the northern ice- 

 sheet. By some such means, provided great accuracy were used, we should obtain a 

 more reliable result than can ever be achieved by the study of archaeological evidence. 



Miss Gareod gave as her contribution to the discussion a studj"^ of the evidence 

 that led her to identify a relatively late Pleistocene pluvial period in Palestine. 



Dr. G. C. Simpson, C.B.E., F.R.S., suggested that it is probable that there are 

 large variations of solar radiation which, as a first approximation, we maj^ consider to 

 be periodic. During the periods of maximum radiation the climate of the world as a 

 whole is warm and wet, while durmg the periods of minimum radiation it is cold and 

 dry. The effect of these changes varies from place to place. On the borders of a 

 region where ice forms in the winter, the effect will be as follows. With the solar 

 radiation at its minimum the temperature will be low, but owing to the absence of 

 cloud and precipitation there will be little or no accumulation of snow, the winters 

 will be cold and the summers warm. The conditions will give rise to steppes. 



As the radiation increases there is more snow-fall and ice-sheets develop. As the 

 radiation increases still further, the mean temperature rises. More rain falls but 

 less snow, and the melting is increased. Finally, when the temperature and rainfall 

 are at their maximum all ice may disappear — probablj'^ right to the poles. A complete 

 oscillation of solar radiation will lead to one warm and wet epoch, one cold and dry 

 epoch and two advances and retreats of the ice. 



There appear to have been two such oscillations of solar radiation during the 

 Pleistocene period. In North-west Europe the Pleistocene period came in with low 



