viii PREFACE TO FIRST EDITION. 



vania (our report constitutes Yol. Z of the Second Geologi- 

 cal Survey of that State). The summers of 1882 and 1883 

 were spent under the auspices of the Western Eeserve His- 

 torical Society of Cleveland, Ohio (whose secretary, Judge 

 C. C. Baldwin, had the sagacity to recognize, at ttat early 

 time in the investigations, the historical bearing of the 

 work), in continuing the survey across Ohio, Kentucky, and 

 Indiana (see my report to that society, 1884, and an article 

 in the "American Journal of Science," July, 1883). Dur- 

 ing the summers of 1884 and 1885 I was employed, as a 

 member of the United States Geological Survey, in tracing 

 the boundary across Illinois, and in reviewing the field in 

 Ohio and western Pennsylvania. The report of this work 

 has not yet been made public, but permission to use the 

 facts has been generously granted by the director of the 

 survey, Major J. W. Powell. The summer of 1886 was 

 spent in Washington Territory, and upon the Muir Glacier 

 in Alaska. The two following seasons were occupied in 

 further exploration of Ohio, Dakota, and other portions of 

 the Northwest. Thus I have personally been over a large 

 part of the field containing the wonderful array of facts of 

 which I am now permitted to write. 



In the autumn of 1887 I was invited to give a course 

 of lectures upon the Ice Age in North America before the 

 Lowell Institute in Boston, and in the following year be- 

 fore the Peabody Institute in Baltimore. For the informa- 

 tion of the audiences who heard those courses of lectures it 

 is proper to say that the present treatise incorporates all 

 the facts then presented, though in a different form. The 

 volume covers, however, a much wider field than the lect- 

 ures, and is more ample in its treatment of all the topics. 



But it is not to be supposed that a single person can 



