384 SECTIONAL TRANSACTIONS.— H. 



radiation and a cold dry epoch (the Weybourne Crags) then the ice advanced on 

 account of increased precipitation (Giinz Glaciation) only to retreat as the radiation 

 and temperature increased, bringing in a warm wet epoch (the Cromer Forest Bed). 

 The maximum of solar radiation was passed and the temperature and precipitation 

 decreased. On account of the decreasing temperature ice formed and advanced 

 (Mindel Glaciation), but as the precipitation decreased the ice retreated and there 

 was a cold, dry interglacial epoch (Mindel-Riss Interglacial). In this epoch the 

 minimum of solar radiation was passed and the ice advanced again (Riss Glaciation) 

 and retreated as the temperature rose, leading to the second warm interglacial epoch 

 (the Riss-Wiirm Interglacial). The sequence continued with another glacial epoch 

 (the Wiirm Glaciation) followed by another cold interglacial epoch (this gave rise 

 to the steppe conditions in North-west Europe associated with the Magdalenian 

 Culture). The present conditions in Europe were introduced by a drift of the Pole ; 

 but the world as a whole is still in a cold, dry interglacial epoch. 



According to this sequence there should have been during the Pleistocene period 

 two pluvial periods of world-wide extent correlated with the Giinz-Mindel and the 

 Riss-Wurm interglacial epochs respectively ; and three arid periods, the first before 

 the Giinz Glaciation, the second during the Mindel-Riss interglacial epoch and the 

 third at the present time. 



Dr. C. E. P. Brooks said that, in considering the various bases of correlation of 

 Quaternary events in different parts of the world, stratigraphy, palseontology, 

 archaeology — we must not forget that the succession of climatic changes may also 

 have a high correlation value. A large ice-sheet, because of its high reflective power 

 for solar radiation and high emission of terrestrial radiation, is a powerful cooling 

 agent, and winds blowing outwards from the surface extend the cold over a large 

 area. The existence of an ice-sheet covering Scandinavia and the Baltic would, 

 therefore, cause " sympathetic " glaciation of the Alps. Where ice-sheets ended in 

 the sea, the latter was cooled by the melting ice, and this must have extended the area 

 of cooling still more widely, and finally, the presence of extensive areas of ice must 

 have profoundly modified meteorological conditions in all parts of the world. Glacial 

 phenomena were developed in a large number of places in all continents from the 

 Equator to the Poles. Such a widespread distribution implies a general cause rather 

 than a series of independent local causes. Hence, whatever the cause actually was, 

 and it is not unlikely that two or more causes, geographical and cosmic, operated 

 together, it is a priori highly probable that the main glacial stages were contemporaneous 

 in all parts of the world. Support, if any is needed, is provided by the researches of 

 de Geer and his collaborators, who have shown that the final retreat of the glaciers was 

 probably contemporaneous in Europe, Iceland, North America, the Argentine and 

 the Himalayas. 



Deposits indicating the presence of more water are as widespread as those indicating 

 more ice. Thus, in regions which were not glaciated we can distinguish a Pluvial 

 period, which is definitely of Pleistocene age and to that extent roughly synchronous 

 with the Glacial period. Unfortunately, pluvial and glacial phenomena are typically 

 developed in different regions, but in western U.S.A. the greatest extension of the 

 Sierra Nevada glacier ended in old Lake Mono when the latter also attained its 

 maximum development. For the present, however, the correlation of the various 

 stages of pluviation and glaciation must rest mainly either on archaeological evidence 

 or on meteorological considerations. 



The amount of water actually in the atmosphere at any time is relatively very 

 small, hence the total annual rainfall over the globe must be equal to the total annual 

 evaporation. 



Whatever the initial causes, there is little doubt that the great fall of temperature 

 in high and higher-middle latitudes was due largely to the ice itself, on land and sea, 

 and that in tropical regions temperature during the glacial periods was little, if at all, 

 lower than at present. There was a great increase in the temperature difference 

 between low and high latitudes and this must have led to greater wind movement, 

 both horizontally and, because of the increased storminess, vertically. This must 

 have increased the evaporation and consequently also the rainfall. Over the great 

 ice-sheets themselves, however, conditions must have been largely anticyclonic and 

 the total water precipitated less than at present, still further increasing the rainfall 

 over the non-glaciated regions. The most marked changes would be expected on the 

 equatorial flanks of the ice-sheets, as on the southern side of the Alps, and within the 



