METHOD OF INVESTIGATION 3 



bottom rather soon, but for the most part the finest particles 

 remained suspended for a long time, and settled during the 

 late fall and winter. Consequently, at first silt and coarse clay, 

 then finer and finer clay, were deposited on the lake bottom 

 during a year. The silty part, however, contains a considerable 

 quantity of rather fine particles, which evidently were pulled 

 down by those of greater size (Oden, 1920, p. 339) . 2 Accordingly, 

 the sediments of the year became clearly separated from those 

 of the preceding year. These annual layers are the layers called 

 vanes. Clays derived from fine-grained slates or deposited 

 during a time of very little melting and slow current, however, 

 are sometimes practically homogeneous, because even those 

 parts deposited during the summer are greasy. 3 



If, on the contrary, the glacial river discharged into salt or 

 strongly brackish water, as was the case on the Swedish west 

 coast and on the Atlantic coast north of Boston, the ice water 

 rose to the surface because of its lower specific gravity. On 

 account of the salinity even the finest material settled rather 

 soon; and on the sea bottom a more or less homogeneous clay 

 was deposited, a clay in which large grains are mixed with the 

 very finest. It follows that marine clays show no varves. 



Method of Investigation 



That the distinct period of time recorded by each layer is the 

 year was suggested, as it seems independently, by several 

 American and Swedish geologists, by Alfred Smith in 1832 

 (p. 229), Edward Hitchcock in 1841 (p. 359), De Geer in 1882, 

 Emerson in 1887 (p. 404), Upham in 1888 (p. 132), and Taylor 



2 Publications are cited thus throughout this work. For full titles see List of 

 References at the end of the volume. 



3 Deposition of glacial varve clay evidently ceased when the land ice had dis- 

 appeared. In the fiords in northern Sweden, however, deposition of another kind 

 of annually laminated clay followed. This clay, on which the post-glacial chronology 

 is based, is silty and very thinly laminated and shows only faint difference between 

 the two zones which mark the year. The upper dark gray zone, the equivalent of 

 the winter layer in the glacial varve clay, is essentially deposited in connection 

 with the flood of the rivers during the melting of the snow in spring (Liden, 191 1, 

 p. 273). 



