INTRODUCTION xiii 



as chairman of the Division of Geology and Geography of the 

 National Research Council, has done much to raise funds for 

 the field work and to interest geological surveys in the northern 

 states. Mr. Sayles has kindly supported the preparation and 

 printing of the illustrations. The American Geographical 

 Society put me in a position to work up my material into this 

 form and has attended to its publication. 



