6 SEASONAL DEPOSITION IN AQUEO-GLACIAL SEDIMENTS. 
The first mention that has come to my notice, of the idea that these regular 
layers might mean years, was made by Edward Hitchcock in 1841. He wrote: 
“The layers of our diluvial clay rarely exceed half an inch in thickness in the valley of 
the Connecticut. In each layer the coarsest part of the materials is invariably placed at 
the bottom; and there is a gradual diminution of fineness upward, until at the top it is ex- 
ceedingly fine clay. This arrangement is just as we might expect from deposition in water; 
and it shows perfectly quiet water. Probably each layer marks the annual deposit; or the 
result of a freshet.”” E. Hrrcncock, 1841, 2, p. 359, 360. 
These words were written just before Hitchcock accepted the theory of 
the Glacial period as expounded by Agassiz and Charpentier in 1835. It is 
sufficient to realize that the regular layers were considered at an early date. 
In Europe, during 1878 de Geer noted the regular banding in the glacial 
clays of Sweden and attributed their regularity to annual or seasonal deposition. 
To de Geer more than to anyone else we owe the firm foundation on which the 
theory of seasonal or annual deposition in these glacial clays rests. He was 
the first geologist to explain the origin of the banding and also the first to prove 
the truth of his theory. For many years he worked toward the solution of 
the problem and he gave a preliminary account in a lecture before the Geo- 
logical Society of Stockholm in 1884. Not until 1912, however, did he publish 
his results in detail. 
At the International Congress of Geologists at Stockholm in 1910 de Geer 
read an impressive paper, A geochronology of the last 12,000 years (de Geer, 
1912), a paper so important that I quote significant parts of it here: 
“Geology is the history of the earth, but hitherto it has been a history without years. 
It is true that many attempts have been made to obtain time-computations for certain parts 
of that history, but none of them has been capable to stand a closer trial. Thus, the very 
able authors [Chamberlin & Salisbury] of one of our lately published textbooks of geol- 
ogy say (1): ‘The desire to measure the great events of geological history in terms of years 
increases as events approach our own period and more intimately affect human affairs. The 
difficulties attending such attempts are, however, formidable, and the results have an un- 
certain value. At best they do little more than indicate the order of magnitude of the periods 
involved. Geological processes are very complex, and each of the co-operating factors is 
subject to variations, and such a combination of uncertain variables introduces a wide range 
of uncertainty into the results.’ 
“Under such circumstances it may be suitable here to place briefly before you a new, 
exact method of investigation, through which it is possible, by actual counting of annual 
layers, to establish a real geochronology, for a period reaching from our’ time backwards 
some 12,000 years. 
“As a basis for this chronology have been used certain late glacial and postglacial, 
periodically laminated sediments in which the deposition for every single year can be dis- 
criminated. By actual countings and successive combinations of a great number of sections 
