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Boundless treasure: the thrill of literature study

Author: Paul Meijer, Department of Earth Sciences, Utrecht University (

This winter I was reading Patrick Leigh Fermor’s account of the first stretch of his walk from Hook of Holland to, as he insisted on calling it, Constantinople. Starting in December 1933 and roughly following the Rhine and the Danube, it would take him a year and a half to arrive at his destination. A few years earlier, in 1927, a book was published that would certainly have been available at the libraries of the university towns that Leigh Fermor passed through: a monograph entitled “Die Straße von Gibraltar” written by geographer Otto Jessen. On my desk is the copy a student of the time would have taken out of the library of Humboldt University of Berlin. It has “ausgesondert” (removed from collection) stamped all over it. I came to seek out this book after the progress report given by Beatriz during our online meeting in the first week of March. But Jessen (1927) was not the first old book that I turned to because of this talk.

               To introduce her topic, Beatriz showed a map of the Mediterranean Sea as prepared in the context of the Atlantropa project. This was the idea launched in 1928 by the German engineer Herman Sörgel (1885-1952) to build a dam across the Strait of Gibraltar and use the sea-level difference anticipated to result from this, to generate hydroelectric power. The map shown by Beatriz brought up the question: since when do we actually know the bathymetry of the Mediterranean Sea? My copy of the 1912 report on the Danish oceanographical expeditions to the Mediterranean Sea (Schmidt, 1912), “ausgesondert” by the university library of Würzburg and in surprisingly good shape if we disregard the desiccated slice of salami I had to cut from one of its pages, gave part of an answer. Already in 1912 the depth of the shelves and many slopes were charted and the deepest portions fathomed spotwise. In fact, much of this knowledge appears to originate with surveys undertaken at the end of the 19th century by the British Admiralty.

E-mailing about the map and the Atlantropa project in general with Beatriz and Angelo, other questions came up. It is obvious that Sörgel knew that, without a connection to the Atlantic Ocean, the level of the Mediterranean Sea will go down because its freshwater budget is dominated by evaporation. But where did he base this on and was he perhaps aware of the Messinian Salinity Crisis? While I found no confirmation of the latter, Alexander Gall in his 1998 dissertation on Sörgel’s “stranded vision”, does talk about issues addressed in the project that are remarkably parallel to our thinking about the salinity crisis. For example, the insight that an inflow of Mediterranean water is required to keep its sea level constant once it has fallen far enough. Or calculations of the rate of salinity increase of the basin in response to closure. It was even speculated that the disappearance of a dense outflow from Gibraltar would lead to changes in Atlantic circulation. Much has been written about the project already, including the societal and political context in which it was conceived (e.g., Gispen, 2001; see Daniel’s book chapter with Ricarda Vidal for more on the parallel to the MSC). Important for us now is that Gall (1998) states what he thinks was Sörgel’s main source on matters oceanographic. And this brings us to Jessen (1927).

               Printed on thick paper in which each letter forms a slight depression, the book is beautiful in its breadth of topic also. Geography, oceanography (leaning heavily on the Danish 1912 report), geology and also history of the region centred on the Strait of Gibraltar are combined in a natural way. On page 101 we find the notion that if somehow disconnected from the ocean the level of the Mediterranean will drop. What is more, citing Ramsay and Geikie (1878) for evidence from the mammal-fossil record, Jessen presents the idea which, according to Gall (1998), was a main inspiration for Sörgel, that a land bridge actually extended across Gibraltar during the Quaternary (more on Sörgel’s inspiration in Garcia-Castellanos and Vidal, 2014).

               Scanning the book specifically for the latter bit of information, my attention was drawn to the section entitled “Formation and age of the Strait of Gibraltar”. This, however, proves to treat the older history of the region. To my surprise it relates the insight that, prior to the current Strait, two corridors existed, one north of the Betic mountains of southern Spain, the other south of the Moroccan Rif, and that both corridors were closed at some point in the Late Miocene and it was in the Pliocene that the Strait of Gibraltar opened. This in a book from 1927! Although aware that our favourite evaporites were known from land sections well before Maria Bianca Cita, Bill Ryan and Ken Hsü established the basinwide extent of the crisis during DSDP Leg 13, I was still under the impression that the notion of a Pliocene opening of the Strait of Gibraltar originated with the latter authors. Jessen is less than generous with references but footnotes suggest that Gentil (1909) and, judging from the title, in particular, Bergeron (1909) are his main source, taking us back another 18 years. As a matter of fact, in their reflection on the DSDP cruise and its direct aftermath, Hsü et al. (1973) list a 1918 paper by Gentil as their oldest reference in support of the statement that “a Late Miocene Mediterranean ‘salinity crisis’ had been recognized”.

               It transpires that French geologists had already in the early 20th century interpreted the Neogene stratigraphy of southern Spain and Morocco in terms of the evolving connections. Much of the insight and in particular the notion that the Strait of Gibraltar came into existence in the Pliocene, appears to go back to a geological expedition (“Mission d’Andalousie”) undertaken by the French Academy of Sciences to survey the region after an earthquake that happened 25 December 1884. The Pliocene origin of the Strait of Gibraltar (Michel-Lévy and Bergeron, 1888; Bergeron, 1909) was inferred from the presence of Atlantic-type fauna in Pliocene sediments to the east of the Strait, in combination with the insight that the Betic and Rif corridor had by that time already closed. According to Bonnin et al. (2002) it was Marcel Bertrand (well known for his work in the Alps and also a member of the expedition) who was one of the first to link the Late Miocene absence of a connection to the presence of gypsum deposits.

               In each of the cases we have looked at, tracing back the origin of the ideas landed us in the late 19th century. Further research will certainly unearth older foundational work. It is relevant to be aware of how much was already known or discussed by our predecessors. Although it is easy to overlook a source or misinterpret a development, we should always try to properly acknowledge previous workers. But most of all, there is a special pleasure in this unravelling of history. Throughout his adventure, Patrick Leigh Fermor managed to get himself invited to the mansions of rich families. His favourite pastime was to explore their libraries. Writing in the second book about his journey, “As far as I was concerned, boundless treasures beckoned.”


Thanks are due to Beatriz and Ronja for encouragement and suggestions.


Bergeron, J., Sur l’âge de la formation du détroit de Gibraltar, Bull. Soc. géol. France, ser. 4, vol. 9(1-9), 228-229, 1909.

Bonnin, J., M. Durand-Delga and A. Michard, La “Mission d’Andalousie”, expédition géologique de l’Académie des sciences de Paris à  la suite du grand séisme de 1884, C. R. Geoscience, 334, 795-808, 2002.

Gall, A., Das Atlantropa-Projekt; Die Geschichte einer Gescheiterten Vision: Hermann Sörgel und die Absenkung des Mittelmeers, Campus Verlag, Frankfurt, 187 pp., 1998.

Garcia-Castellanos, D. and R. Vidal, Alternative Mediterraneans six million years ago: A model for the future?, in: R. Vidal and I. Cornils (Eds.), Alternative Worlds; Blue-Sky Thinking since 1900, Peter Lang, pp. 53-71, 2014.

Gentil, L., Notes sur la géologie du Maroc, Bull. Soc. géol. France, ser.4, vol. 9(1-9), 220-227, 1909.

Gentil, L., Sur le synchronisme des dépôts et des mouvements orogéniques dans les détroits Nord-Bétique et Sud-Rifain (Espagne méridionale et Maroc), Comptes rendus Acad. Sci. Paris, 167, 727-730, 1918.

Gispen, K., Das Atlantropa-Projekt; Die Geschichte einer gescheiterten Vision: Hermann Sorgel und die Absenkung des Mittelmeers (review), Technology and Culture, 42 (3), 596-598, 2001.

Hsü, K.J., M.B. Cita, and W.B.F. Ryan, The origin of the Mediterranean evaporites, in: Ryan, W.B.F., K.J. Hsü and M.B. Cita (Eds.), Initial Reports of the Deep Sea Drilling Project, 13, Part 2. U.S. Government Printing Office, Washington D.C., pp. 1203–1231, 1973.

Jessen, O., Die Straße von Gibraltar, Dietrich Reimer Verlag, Berlin, 283 pp., 1927.

Leigh Fermor, P., A Time of Gifts, New York Review Books, New York, 321 pp., 1977.

Leigh Fermor, P., Between the Woods and the Water, New York Review Books, New York, 264 pp., 1986.

Michel-Lévy, A and J. Bergeron, Étude géologique de la Serrania de Ronda, in: Académie des sciences de Paris (Ed.),  “Mission d’Andalousie”: études relatives au tremblement de terre du 25 décembre 1884 et à la constitution géologique du sol ébranlé par les secousses, Mém. Acad. Sci. Paris, 30 (2), 171-383, 1888.

Ramsay, A.C., and J. Geikie, On the geology of Gibraltar, Quart. J. Geol. Soc. London, 34, 505-541, 1878.

Schmidt, J. (Ed.), Report on the Danish Oceanographical Expeditions 1908-1910 to the Mediterranean and Adjacent Seas, Høst & søn, Copenhagen, 269 pp., 1912.


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