Geoscience Reference
In-Depth Information
contained in Harmer's 1901 paper, had been shown to be untenable due to research
by the Swedish geologist, Gerard De Geer (1858-1943) and other workers on
varves (distinct layers of sediments deposited annually in glacial lakes); the latest
glacial stage was certainly contemporaneous on both sides of the North Atlantic.
As Harmer would no doubt have accepted this view, Brooks thought it best to
delete any passages which depended on this supposed alternation of glaciations. In
other respects the text was practically unchanged.
In supplying a figure that was missing from the manuscript, Brooks endeav-
oured to interpret Harmer's views as depicted in those of his 1901 paper, showing
surface pressure patterns and prevailing wind directions in the Northern Hemi-
sphere during the maximum Pleistocene glaciation of Europe. Brooks mentioned
that the construction of this new figure required some explanation. Its purpose was
to show how by elevation a ridge of land was formed connecting Greenland with
Europe. Although Harmer had supposed that at the same time the northern part of
North America was depressed below its present level, Brooks noted that this was
probably not the case and accordingly suggested the following compromise:
between Greenland and Scandinavia the land was supposed to have extended to the
submarine contour of 1,000 m (3,300 ft) below sea-level; on the west coast of
Greenland, the east and north coasts of North America, the American Arctic
Archipelago, the British Isles and France, the submarine contour of 200 m (660 ft)
below sea-level has been taken as the limit of the former land extension. Elsewhere
(including Svalbard) no change was made, except that Brooks followed Harmer in
indicating the existence of an Antillean extension of the North American conti-
nental area.
Harmer began his paper by stating that when the distinguished geologist, Sir
Charles Lyell (1797-1875) discussed the possible effect of astronomical causes on
past climates (particularly that of the Pleistocene epoch) in the 10th edition of his
Principles of Geology (1868), he reverted to the theory he had proposed over 30
years earlier in the first edition of his volume, that it is only by admitting the
frequent and paramount importance of geographical changes on the earth itself
(such as variations in the height and position of the land and the course of ocean
currents) that those great revolutions of climate can be explained 'which wrapt
large portions of the Northern Hemisphere in a winding sheet of continental ice'
(Fleming 1998 ).
Harmer would also have been aware that in his Principles of Geology Lyell
stated that in the present period the oceans have free communication over the whole
globe; as a result the warm waters of the equator can penetrate to the poles and the
annually accumulated ice of the Arctic regions is melted by such warm southern
currents. But suppose, Lyell suggested, the Arctic and north temperate sea were
completely, or almost enclosed by land, as might easily occur by a comparatively
limited elevation of the sea bed between Greenland, Iceland and the Orkney Islands,
and at the entrance to the Davis Strait, would not the ice, he queried, of each
successive winter accumulate so as to form a vast ice cap which would inevitably
produce a glacial epoch over the whole north temperate zone. Therefore changes in
the distribution of sea and land are a sufficient cause, Lyell believed, for any
Search WWH ::




Custom Search