PREFACE ix 



The student of glacial history, particularly in New England 

 and New York, will discover in this study an amazing array of 

 conclusions. Dr. Antevs has traced a series of clay layers which 

 mark approximately 4,000 successive years up the Connecticut 

 Valley from Hartford, Conn., to St. Johnsbury, Vt. He has found 

 large parts of the same series duplicated in the Hudson and Merri- 

 mac Valleys. He has worked out successive positions of the reced- 

 ing ice border, after only a few months of field work, in a region 

 where two generations of American geologists, baffled by the ab- 

 sence of definite moraines, have realized little or no success. The 

 estimate of time occupied by this recession is a simple arithmetical 

 count, expressed not in centuries but in years. Such accuracy 

 can never be claimed for our computations of time from the 

 Niagara gorge, where large factors are only imperfectly measur- 

 able. An investigation so precise in method and execution and 

 so suggestive will give fresh impulse to our studies of Pleistocene 

 glaciation. There is scarcely a problem of the history of this 

 curious and interesting period that Dr. Antevs' work does not 

 touch. It suggests, for instance, where we should look for reces- 

 sional moraines and how moraines at widely separated points 

 should be correlated. It stimulates more thorough study of the 

 records made in flooded valleys and ponded lakes, with their 

 shifting complicated outlines, and of the upward and downward 

 warpings of the region which accompanied the withdrawal of 

 the ice sheet. It assigns to each deposit its proper date, which, 

 while not as yet connected with later records so as to permit it to 

 be expressed as so many years "B.C.," is nevertheless as accurately 

 referred to a certain point in the glacial period as dates of human 

 history are referred to the beginning of the Christian era. 



The larger number of readers, who are not specialists in geology 

 but who are interested in the measurement of time, in prehistoric 

 climate, and in the migrations of plants and animals, will see in 

 these geochronological studies a key which, if properly used in 

 other regions, may settle, better than any other means yet 

 found, the question whether ice sheets on different continents 

 were contemporaneous or not. The attitude of Dr. Antevs 



