896 EMILIANI AND FLINT [CHAP. 34 



suggest the likelihood that earlier events were also similar, but the scanty data 

 published thus far are compatible with the view that the last major glacial age 

 included, in North America, a long sequence of events antedating those of 

 the classical Wisconsin glaciation. 



D. Temperatures 



Examination of geologic sediments and other features of Pleistocene age has 

 shown that many such things are not in equilibrium with their present climatic 

 environment. Glacial drift is widespread in middle latitudes, even in positions 

 close to sea-level. Terrestrial plants and animals occur as fossils in areas where 

 climatic parameters, such as temperature and precipitation, preclude their 

 existence today. Ancient soils, both buried and at the present surface, and 

 chemical precipitates such as travertines are known to be out of equilibrium 

 with existing climates, chiefly as regards precipitation values. In some regions 

 deflation basins and extensive sand dunes are widespread, now fixed by a 

 continuous cover of vegetation. The shorelines and sediments of former lakes 

 are conspicuous in some regions now arid. Artifacts recording the industries 

 of prehistoric man occur in areas now too dry to support similar cultures. The 

 occurrence of identical species in habitats widely separated by inimical terrain 

 suggests former continuity of habitat. 



Disequilibrium features of this nature establish the fact of widespread 

 change of temperature or precipitation or both, within the general span of 

 Pleistocene time. Most of the evidence jDertains to temperature rather than to 

 precipitation. Although in a very few instances the data are sufficiently good to 

 indicate the approximate amplitude of change, on the whole they are both 

 widely scattered and imprecise. It is impossible as yet to correlate them from 

 one region to another. 



The data are both physical and organic. The physical group consists of changes 

 in the vertical or areal ranges of parameters that are temperature-dependent at 

 least in part. One of the earliest of these parameters to be recognized is fluctua- 

 tion of the altitudinal zone within which nivation sculjDtures cirques. In the 

 northern Alps, during the Wiirm glaciation, the zone was depressed to as much 

 as 1200 m below its present position. A comparable depression (1200 m) is 

 indicated for the Wisconsin glacial maximum in the Rocky Mountains of 

 Colorado, and a depression of at least 1000 m occurred on Mt. Kenya at the 

 equator. Translation of these data into terms of temperature change is not yet 

 possible because the climatic snow-line is dependent also on precipitation. Based 

 on lapse rate alone, without correction, the temperature difference equivalent 

 to a snow-line difference of 1200 m would be about 6.6°C. 



The occurrence of glacial drift beyond the present range of glacier ice implies 

 that surface temperatures were no greater than 0°C at the time and place of 

 deposition. Zero temperature at a glacial maximum in Illinois, at 38°N and at 

 an altitude of less than 150 m, compares with around 13°C today. Such tem- 

 peratures, however, were dependent partly on the presence of the glacier itself 

 and so were not necessarily secular in an independent sense. 



