Of
Latitude, Or 450 Miles, Of A Harbour, Where Three Species Of
Oliva, A Voluta, And A Terebra, Are The Commonest Shells,
Within Less Than 9 Degs.
From where palms grow, within 4.5 degs.
of a region where the jaguar and puma range over the
plains, less than 2.5 degs.
From arborescent grasses, and
(looking to the westward in the same hemisphere) less than
2 degs. from orchideous parasites, and within a single degree
of tree-ferns!
These facts are of high geological interest with respect to
the climate of the northern hemisphere at the period when
boulders were transported. I will not here detail how simply
the theory of icebergs being charged with fragments of rock,
explain the origin and position of the gigantic boulders of
eastern Tierra del Fuego, on the high plain of Santa Cruz,
and on the island of Chiloe. In Tierra del Fuego, the greater
number of boulders lie on the lines of old sea-channels, now
converted into dry valleys by the elevation of the land. They
are associated with a great unstratified formation of mud
and sand, containing rounded and angular fragments of all
sizes, which has originated [15] in the repeated ploughing up of
the sea-bottom by the stranding of icebergs, and by the matter
transported on them. Few geologists now doubt that
those erratic boulders which lie near lofty mountains have
been pushed forward by the glaciers themselves, and that
those distant from mountains, and embedded in subaqueous
deposits, have been conveyed thither either on icebergs or
frozen in coast-ice.
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