Geer, Gerhard Jakob De

(b. Stockholm, Sweden, 2 October 1858; d. Saltsöbaden, Sweden 23 July 1943)

geology, geochronology.

Geer belonged to one of the leading noble families in Sweden. Originally from Belgium, they settled in Sweden at the beginning of the seventeenth century, and many of them have since then been important in politics and economics. Both his father, Louis de Geer, and his older brother, Gerhard Louis de Geer, were prime ministers of Sweden (1858–1870, 1875–1880 and 1920–1921, respectively), and his father was the leading politician in Sweden in the last half of the nineteenth century. Geer himself was also involved in politics and was a member of the Swedish parliament from 1900 to 1905.

Geer grew up in a home which was a center for both the political and the cultural life of Stockholm. He received his master’s degree in geology from Uppsala in 1879, having been appointed to the Swedish Geological Survey in 1878. After a few years of ordinary geological mapping, Geer turned his concentration to what was to be his lifetime interest, the study of Quaternary (Pleistocene) geology. The first main problem was that of raised beaches. Shorelines much above sea level were known both in Scandinavia and in other regions, but the complicated system by which they were uplifted isostatically was not understood. The rise of the land is highest where the ice was thickest and the depression largest. The uplift decreases in all directions from the center of glaciation. Superposed on this is the eustatic change in sea level, due partly to the melting of inland ice. This complicated system was discovered and elegantly described by Geer, who also coined the term “marine limit” (the highest shoreline of the sea at any particular locality). The summary of his work, published in 1896, was one of the classic works in Scandinavian geology.

In order to explain glacial phenomena Geer traveled to Spitsbergen, where glaciers somewhat similar to the Quaternary ones still exist. He took part in and led expeditions in 1882, 1896, 1899, 1901, and 1908, among them the Swedish-Russian meridian expedition, which he led. Geer introduced terrestrial photogrammetry as an aid in his studies, and it was later used by most other Arctic expeditions, in order to increase the precision of both geological and geodetical observations. In 1897 Geer became professor at the University of Stockholm and was its president from 1902 to 1910. At Stockholm he established the varve chronology. Varves are annual, cyclic sediments consisting of summer and winter bands of silt and clay deposited by glacial meltwater in fresh or brackish water. They vary in thickness, and Geer early had the idea that these variations could be used by correlating various sections through varve sequences. In 1904–1905 he had his students measure all varves in a 200-kilometer-long north-south section near Stockholm; they found that the last ice in the area had melted away over a period of 800 years and that they could pinpoint the position of the ice margin for every year. This system was soon extended from Scania to the mountains of central Scandinavia, where it covered a period of 15,000 years. Geer used the final stage of the melting of the inland ice as his zero year; later studies by his assistant Ragnar Lidén made in the Angerman River, where varves are formed today, showed that the zero year was 6739 b.c. Geer’s varve method is cumbersome and restricted to the few areas where varves are found, but it gives an unprecedented accuracy in age determinations. Geer became worldfamous when he presented his results at the International Geological Congress at Stockholm in 1910, but his final paper on the subject, “Geochronologica Suecica,” did not appear until 1940.

In 1924 Geer retired and became head of the Institute of Geochronology at the University of Stockholm. After several years of travel he and a number of assistants tried to extend his system on a global scale. These “teleconnections” were not generally accepted, since it seemed unlikely that the variations in meltwater and sediment volume should be synchronous all over the globe. Geer worked intensely during his last years to reline his method and to prove his long-distance correlations. After his death studies by isotope methods (carbon 14) have shown that some of his correlations, especially those with North America, were remarkably precise.

BIBLIOGRAPHY

I. Original Works. Complete bibliographies of Geer’s more than 200 scientific publicationsate in Nilsson and in Post (see below). Geer’s most important works were Om Skandinaviens geografiska utveckling efter istiden (Stockholm, 1896), written in unusually clear and lucid Swedish but not a popular book and not easily accessible to non-Scandinavians; and “Geochronologica Suecica, Principles,” Kungliga Svenska vetenskapsakademiens handlingar, 3rd ser., 18 , no. 6 (1940).

II. Secondary Literature. The best biographies of Geer are E. Nilsson, “Gerhard de Geer, geokronologen,” in Levnadsteckningar över Kungliga Svenska vetenskapsakademiens ledamoter, 172 (1969), 213–250; and L. von Post, “H. J. de Geer,” in Svensk biografisk lexikon, X (1931). 564–567.

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