GEOCHRONOLOGY, AS BASED ON SOLAR RADIATION, 

 AND ITS RELATION TO ARCHEOLOGY ' 



By Gerard De Geer 



In the American journal Science for 1920 mention was made of 

 my plan for investigating certain laminated clays in North America. 

 During a previous visit to that country in 1891 I had noticed, in 

 several places, laminated clays, similar to late glacial melting sedi- 

 ments in Sweden; these I had found, by long continued investiga- 

 tions, to represent the annual deposit from the melting water along 

 the border of the retreating ice edge. (Fig. I.) With the aid of a 

 graphic method for the comparison of the sharply marked annual 

 layers or varves, I had succeeded in identifying such varves from one 

 point to another, and ultimately worked out a systematic plan for the 

 elaboration of a continuous time scale. (See p. 690.) This was 

 mainly carried out in 1905-6 on the basis of field measurements 

 made with the assistance of a number of able young geologists. 

 During the following year this standard scale was completed at 

 many points. I thus succeeded in tracing, step by step, the recession 

 of the ice edge and the immediately following progress of the clay 

 varves over one region after the other, until the whole line from the 

 south to the center of Sweden had been traced. 



As might be expected, the lowest and oldest clay varves were 

 found deposited in the southern extremity of the land, while the 

 great ice sheet covered the whole of the rest. By following the 

 progress of the clay, step by step, the whole series was built up, thus 

 forming a continuous and exact time scale for the last recession of the 

 ice through Sweden up to a certain year, when a great ice-dammed 

 lake in central Sweden was drained off, depositing a very thick 

 annual varve. This year was chosen as representing the very end 

 of the late glacial epoch. (See map on p. 691.) 



For many years I tried in vain to find some means of determining 

 the length of the succeeding post-glacial epoch proper, until one of 

 my most successful assistants, R. Liden, discovered in the northern 

 part of Sweden annual varves for that epoch also. Of these varves I 

 measured in one section at the Indal River rather more than 3,000, 



1 Reprinted by permission from Antiquity, Vol. II, No. 7, September, 1928. 



687 



