THE 



AMERICAN JOURNAL OF SCIENCE 



[THIRD SERIES.] 



Akt, XLI. — On the Relationship of the Pleistocene to the 

 P re-pleistocene formations of the Mississippi Basin, south 

 of the limit of glaciation;* by T. C. Chambeklin and R. 

 D. Salisbury. 



The deposits made by the ice and by the waters which 

 -originated from it during the glacial period, possess a char- 

 acter so unique, and so markedly unlike that of the under- 

 lying formations within the glaciated area of the United 

 States, that there has been little difficulty in discriminating 

 between them. There have been differences of opinion as to 

 the relative importance of the various agencies which are 

 believed to have been operative in the production of the drift, 

 and in some minor measure these differences still exist. But 

 whether the drift of any particular region be believed to be 

 the work of glaciers, or of icebergs or ice-floes, or of glacio- 

 natant lakes or streams, or the joint work of two or more of 

 these agencies, still the drift, as such, is clearly defined from 

 the underlying strata. In many regions, this is true no less 

 of the valley drift which stretches beyond the glaciated area 

 along the avenues of discharge for the melting ice, than of the 

 unmodified drift upon the extra-valley lands farther to the 

 north, where the drift agent is believed to have been land ice. 



* The writers have worked in such close association in the study of this and 

 of correlated regions, that it is difficult to define their individual work and their 

 respective responsibilities; nor is it important; but they have reasons for stating 

 that the preliminary determination of the salient features of the correlation, and 

 the direction of the investigation, are largely the work of Mr. Chamberlin, while 

 the detailed investigation, the elaboration of results, and the preparation of this 

 article are chiefly the work of Mr. Salisbury. 



Am. Jour. Scl— Third Series, Vol. XLI, No. 245.— May, 1891. 

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