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Thomas Jamieson (1829-1913)

 

 

Scottish sea levels

Thomas F Jamieson and isostasy

Thomas JamiesonIn the first half of the 19th century, scientists began to develop their views on the origins of raised marine features and deposits in Scotland. This process may have begun with a letter to The Scotsman in 1834. An anonymous writer, referring to a bed of shells which had been found above sea level near Barrowstowness (Bo'ness), on the Forth estuary, theorised that they were evidence that the land had risen, rather than the sea had fallen, and it was also suggested that the land had risen unequally across the area involved.
 
Some years later, one of the most famous of Scottish geologists, Thomas Jamieson, developed what we now call the Theory of Isostasy and set the scene for a considerable advance in understanding Scottish sea levels. Jamieson was the Factor of the Ellon Castle estate in North-East Scotland, but had a strong interest in geology and became Fordyce Lecturer in Geology at the University of Aberdeen. In 1865, visiting the Blairdrummond estate near Stirling, he was struck by the sequence of deposits exposed in drainage ditches. Here, he saw, at the base stony clay, probably laid down when a glacier occupied the area during the Ice Age. Resting upon this stony clay was clay containing marine shells, which Jamieson thought had been laid down in the sea. Next, peat occurred above the clay with shells, indicating that the sea had left the area allowing a peat moss to accumulate. Above the peat, silty clay occurred, containing the bones of a whale, clearly indicating that the sea had returned, before once more receding to reveal the present land surface, upon which the great peat mosses of the area, now largely cleared, had developed. Jamieson theorised that the weight of the glaciers had lowered the land surface so that when they retreated the sea was able to flood in to low lying areas, but that the land, now free of ice, rose and carried the sediment to present levels. Later, Jamieson (1882; 1906) showed that the depression of the land beneath ice had probably been proportionate to the thickness of the ice, so that features of the former sea shore today decline in elevation away from the area where ice had been thickest. However, Jamieson never used the term “isostasy”. That was introduced in 1899 by US geologist Clarence Dutton.

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