CHAPTER XIV 



PHYSICAL GEOGRAPHY OF THE PLEISTOCENE WITH 



REFERENCE TO THE CORRELATION OF 



PLEISTOCENE FORMATIONS 



ROLLIN D. SALISBURY 

 The University of Chicago 



The character of the changes which marked the transition from the 

 Tertiary to the Quaternary were somewhat unusual, though not 

 unique as they were once beheved to be. Great as these changes 

 w^re, they were probably not equal in magnitude or importance to 

 the changes which marked the transition from one great era of the 

 earth's history to another. The significant changes at the close of 

 the Tertiary are those which had to do (i) with the height and extent 

 of the land and, perhaps as a result of these changes, (2) with pro- 

 found alterations of climate, bringing on (3) glaciation on an extensive 

 scale, and causing (4) migrations and mutations of life. 



I. THE PHYSIOGRAPHIC CHANGES 



The changes in altitude which affected the North American con- 

 tinent late in the Tertiary have not, in most places, been worked out 

 in such detail as to lead to numerical results in which implicit con- 

 fidence can be placed; but the general tenor of the evidence is har- 

 monious, and the main conclusions are probably correct in their 

 general terms. They may be summarized briefly as follows: 



1. In the eastern part of the continent, the land is generally 

 thought to have stood higher than before by some few hundred feet. 

 If the more extreme views of a few of the geologists who have studied 

 this question are accepted, the excess of elevation over the present was 

 a few thousand feet. 



2. In the larger part of the Mississippi basin, the gain in altitude 

 was considerable, though still on a relatively moderate scale. In the 

 eastern and central parts of the basin it is probably to be measured 

 by a few hundreds of feet, rather than by figures of a larger denomina- 



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