Historical perspectives
1. Catastrophists and Uniformitarians
3. Wright and isokinetics
Thomas Jamieson (1829-1913)
Scottish sea levels
Thomas F Jamieson and isostasy
In
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.