268 ROLLIN D. SALISBURY 



general period of time, England has probably been joined to the con- 

 tinent, and southern Europe to Africa. Submerged valleys on the 

 northwestern coast of Europe, if interpreted in the usual way, indicate 

 elevations several hundred to a few thousand feet greater than those 

 of the present, enough, if some of the estimates are correct, to have 

 connected Europe with Greenland and North America. If such a 

 connection existed, it must have entailed changes in oceanic circula- 

 tion sufficient to have affected the climates of high latitudes in an 

 important way. 



The very considerable changes at the beginning of the Quaternary 

 were followed by a great succession of changes as the period pro- 

 gressed. Some of them reinforced the changes just sketched, and 

 some of them were of the opposite phase. Oscillations of level 

 during the Quaternary have been more carefully worked out along 

 the coast of northern Europe than in America. Unexpectedly enough, 

 evidence seems to point to greater depression during the glacial epochs 

 than during the interglacial. The amount of the determined oscilla- 

 tions of level during the Quaternary range from a few feet to a few 

 hundred feet. 



II. EFFECTS OF PHYSIOGRAPHIC CHANGES ON CLIMATE 



In many parts of the earth, as in the interior and eastern part of 

 North America, in Europe, and elsewhere, the increase of elevation 

 at the end of the Tertiary was probably not sufficient to be of great 

 importance climatically, in a direct way. In other regions, as in the 

 western part of North America, on the other hand, the gain in height 

 was probably sufficient to produce considerable effects directly. 



In an indirect way, the effect of the increase of average altitude 

 of land on climate may have been much more considerable. Erosion 

 was stimulated by the increase of altitude and by the decrease of 

 vegetation due to the causes already mentioned. The increased rate 

 of erosion led to the removal of the residual earths and allu^dum which 

 may well have accumulated on the surface to very considerable 

 thickness, and the removal of these materials from the surface exposed 

 the underlying rock to decay. 



If changes in the constitution of the atmosphere are to be regarded 

 as the cause, or as even one cause of chmatic change, the increase of 



