84 THE JOURNAL OF GEOLOGY. 



application by the difficulty of proving stratigraphic continuity 

 in such a formation as the drift, necessitate the greatest care in 

 their use, and reduce the value of hasty and inexpert conclusions 

 to a minimum. 



IV. Areas Where the Criteria find Readiest Application. 

 The foregoing criteria find their readiest application in 

 regions where a later sheet of drift, suspected of belonging to a 

 later ice epoch, failed to reach the border of an earlier sheet of 

 drift, suspected of belonging to an earlier ice epoch. The ist, 

 2d, 3d, 4th, 5th and loth as enumerated above, find their appli- 

 cation wholly within the area affected by the drift of the sepa- 

 rate epochs, if such there were. While within this general area 

 they may be looked for at any point, they are likely to be of 

 rare occurrence, except along a somewhat narrow belt, say 50 

 to 100 miles, adjacent to the border of the lesser ice advance. 

 The conditions for their occurrence and detection are greatly 

 favored if the lesser drift sheet be the later. The 6th, 7th, 9th 

 and 1 2th criteria might hope for application within the same 

 belt, but especially along a narrow zone on either side of the 

 margin of the later drift sheet. It is along this zone that the 

 types of surface are thrown into sharpest contrast, both as to 

 material and topography. The 8th and iith criteria have still 

 wider limits of application, both within and without the border 

 of the lesser ice advance. Rollin D. Salisbury. 



