SOME GENERAL OBSERVATIONS ON THE WHOLE QUATERNARY. 589 



Some General Observations on the Whole Quaternary. 



1. Cause of the Climate. — This is confessedly one of the most diffi- 

 cult questions in geology. There seems to be no doubt that during the 

 Quaternary there were wide-spread oscillations of the earth's crust in 

 high-latitude regions, and a general coincidence of climatic changes 

 with these oscillations. Furthermore, there is little doubt that the cold 

 and the ice-accumulation were attended with northern elevation, and 

 the moderation of temperature and melting of the ice, with subsidence 

 in the same region. But there are some reasons for thinking that the 

 coincidence of the climatic changes with the crust-oscillations was not 

 exact ; that in many places, at least, the maximum of ice-accumulation 

 was associated ivith subsidence. On this point there has been much 

 confusion and difference of opinion. It seems to us that the differ- 

 ences may be reconciled and the facts well explained by supposing that 

 northern elevation produced ice-accumulation ; ice-accumulation by 

 weight produced subsidence ; subsidence produced moderation of tem- 

 perature and melting of ice, and this last by lightening of load pro- 

 duced re-elevation. But (and this is the important point) the effects in 

 each case lagged greatly behind the cause. This is well known to be 

 true in all cases of accumulated effects, but in this case the lagging is 

 great. On this view the accompanying diagram (Fig. 962) graphically 





PLIOCENE Q U A T E R rsi ^J3_^lZZ 



Fig. 962.— Diagram showing the Relation of Land Elevation and Ice Accumulation. The line a b, 

 course of time, and also the present condition as to elevation and ice. 



represents the facts. It is seen that, at the time of maximum ice, the 

 subsidence had already commenced. To this lagging of effects on ac- 

 count of their self -perpetuation and consequent accumulation, must be 

 added another cause of ap2)arent subsidence, viz., the gravitative at- 

 traction of the ice-sheet on the sea, drawing it northward and raising 

 its level. 



As to the cause of the cold, it is certain that northern elevation 

 would produce cold and depression a moderation of temperature in the 

 regions thus affected. It is probable, also, that in the case of Xorth 

 America and Europe the chilling effect of elevation was greatly in- 

 creased by coincident and probably correlative subsidence of Central 

 America, by which the Gulf Stream was diverted across the Isthmus 

 into the Pacific, thereby depriving the ^N"orth Atlantic of the warming 

 influence of this stream. It is safe to conclude, therefore, that these 

 geographical changes were certainly one cause and probably the main 



