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Early Oceanographic Mapping.
Philippe Buache’s Carte Physique et Profil du Canal de la Manche et d’une partie de la Mer du Nord (1752) is a milestone in the graphic illustration of physical geography. Issued as Plate XIV in the Mémoires de l’Académie Royale des Sciences to illustrate Buache’s celebrated Essai de Géographie Physique, the map visualizes his radical claim that the Earth is structured by contiguous mountain chains—many submerged—that bound vast river basins before plunging beneath the oceans. Here he concentrates on the English Channel and southern North Sea, juxtaposing submarine relief with the adjacent watersheds of France and England to argue that the Loire, Seine, Thames, and Rhine once formed a single fluvial system before the Atlantic breached their valley.
Across the top runs an engraved profile section—in effect a side-on cutaway of the Channel floor—extending west to east from the Atlantic approaches off Cornwall to the Rhine delta. Depths are graduated by isobaths, the first printed use of equal-depth curves on a nautical chart; the same technique (with contour-like shading) is repeated below to map the land’s surface elevations. By marrying these two graphic innovations—bathymetric lines at sea and shaded contours on land—Buache created one of the earliest integrated models of terrestrial and submarine relief.
The map that fills the lower two-thirds of the sheet depicts France’s Loire and Seine basins and England’s Thames basin as converging lobes, whose axes are projected offshore and echoed by dotted submarine “valleys.” Buache’s cartography thus fuses Enlightenment measurement with bold theorizing: coastal soundings, river courses, and mountain chains are deployed as evidence for his concept of an ancestral “Loire–Thames” river whose channel is now the modern English Channel.
Though some contemporaries doubted the notion of drowned continental valleys, the map’s methodological impact was profound. Its contouring informed later bathymetrists such as Alexander Dalrymple and Matthew Fontaine Maury, while its basin-centered view of regional geography influenced Desmarest and Lapie. Today the sheet is prized not only as the earliest printed chart to employ isobaths but also as a landmark in visualizing Earth systems—showing at a glance how landforms, drainage, and seafloor topography interlock across the boundary of land and sea.
Philippe Buache (1700-1773) was one of the most famous French geographers of the eighteenth century. Buache was married to the daughter of the eminent Guillaume Delisle and worked with his father-in-law, carrying on the business after Guillaume died. Buache gained the title geographe du roi in 1729 and was elected to the Academie des Sciences in the same year. Buache was a pioneering theoretical geographer, especially as regards contour lines and watersheds. He is best known for his works such as Considérations géographiques et physiques sur les découvertes nouvelles dans la grande mer (Paris, 1754).
L. Schenk Jansz, or Leonard Schenk, was a member of the Schenk family of engravers. His father, Peter Schenk the Elder (1660-1711) moved to Amsterdam in 1675 and began to learn the art of mezzotint. In 1694 he bought some of the copperplate stock of the mapmaker Johannes Janssonius, which allowed him to specialize in the engraving and printing of maps and prints. He split his time between his Amsterdam shop and Leipzig and also sold a considerable volume of materials to London.
Peter Schenk the Elder had three sons. Peter the Younger carried on his father’s business in Leipzig while the other two, Leonard and Jan, worked in Amsterdam. Leonard engraved several maps and also carried on his father’s relationship with engraving plates for the Amsterdam edition of the Histoire de l'Académie Royale des Sciences.
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