CHRONOLOGY DOUGLASS AND ANTEVS 31 3 



changing cataclysm, the Pleistocene glaciation. You have diligently pursued 

 for many years your investigations of the traces of this event as they exist 

 in North America. Your researches have involved the careful scrutiny of 

 river valleys of the north and the beds of ancient lakes long dry. They have 

 involved millions of exact measurements on the laminated clays laid down 

 by summer meltings of Pleistocene glaciers. From these researches you have 

 measured the severity of North American glaciation. You have determined 

 the length of the ages which have elapsed since glaciation reached its height. 

 You have found indications of the variations which existed in that distant 

 past in the radiation of the sun. 



In recognition of these achievements, the Research Corporation of New 

 York has awarded to you through the Smithsonian Institution a grant of 

 §;2,500. In token of this award I now, as chancellor of that Institution, hand 

 you this commemorative medal, and wish for you equal success in your future 

 researches. . , ■ 



LATE-GLACIAL CLAY CHRONOLOGY OF NORTH AMERICA 



By Eknst Antbvs, Unirersiti/ of Stockholm 

 [With 2 plates] 



Chronology is the framework of history, its units being tlie pigeon- 

 holes in which events, changes, and conditions may be arranged in 

 actual and consecutive succession. It brings order and gives per- 

 spective. Chronology is as vital in geology, the history of the earth, 

 as in human and cultural history. 



In geology, time is still essentially a vague conception. Mostly it 

 is only relative; one formation is older than another because it lies 

 beneath or because it contains more primitive forms of life. Fre- 

 quently, however, time is in a way definite, comprising rough esti- 

 mates in thousands or millions of j^ears. In a few instances it is 

 absolute, with the year as the unit. 



The importance of the time aspect in geology is reflected by the 

 many attempts made to determine it. Especially prominent among 

 the endeavors aiming at absolute age are estimates based on atomic 

 disintegration; on climatic changes combined with astronomical 

 phenomena; on climatic changes alone; on the rate of accumulation 

 of salts and degree of salinity of the ocean and of lakes without out- 

 lets; on the rate of deposition, thickness, and extent of organic and 

 inorganic sediments; on rate and amount of erosion by rivers, by 

 lakes, and by the sea; on the rate and amount of weathering and 

 leaching of rocks and soils; on the rate and amount of changes of 

 level of land; on migrations and alterations of floras and faunas; 

 and on sediments in which the year is recorded by lamination. All 

 these methods have their good purposes. Frequently two or more 

 methods serve to date the same beds or the same phenomena and 

 afford a desirable check on one another. 



