Beagle Expedition (1831-1836); Geology -- South America; Volcanoes
Evidence more or less distinct of a change of level between the land
and water, has been detected on almost all the land on this side of the
globe. Captain Grey, and other travellers, have found in Southern
Australia upraised shells, belonging either to the recent, or to a late
tertiary period. The French naturalists in Baudin’s expedition, found
shells similarly circumstanced on the S.W. coast of Australia. The Rev.
W.B. Clarke finds proofs of the elevation of the land, to the amount of
400 feet, at the Cape of Good Hope. (“Proceedings of the Geological
Society” volume 3 page 420.) In the neighbourhood of the Bay of Islands
in New Zealand, I observed that the shores were scattered to some
height, as at Van Diemen’s Land, with sea-shells, which the colonists
attribute to the natives. (I will here give a catalogue of the rocks
which I met with near the Bay of Islands, in New Zealand:—1st, Much
basaltic lava, and scoriform rocks, forming distinct craters;—2nd, A
castellated hill of horizontal strata of flesh-coloured limestone,
showing when fractured distinct crystalline facets: the rain has acted
on this rock in a remarkable manner, corroding its surface into a
miniature model of an Alpine country: I observed here layers of chert
and clay ironstone; and in the bed of a stream, pebbles of
clay-slate;—3rd, The shores of the Bay of Islands are formed of a
feldspathic rock, of a bluish-grey colour, often much decomposed, with
an angular fracture, and crossed by numerous ferruginous seams, but
without any distinct stratification or cleavage. Some varieties are
highly crystalline, and would at once be pronounced to be trap; others
strikingly resembled clay-slate, slightly altered by heat: I was unable
to form any decided opinion on this formation.) Whatever may have been
the origin of these shells, I cannot doubt, after having seen a section
of the valley of the Thames River (37 degrees S.), drawn by the Rev. W.
Williams, that the land has been there elevated: on the opposite sides
of this great valley, three step-like terraces, composed of an enormous
accumulation of rounded pebbles, exactly correspond with each other:
the escarpment of each terrace is about fifty feet in height. No one
after having examined the terraces in the valleys on the western shores
of South America, which are strewed with sea-shells, and have been
formed during intervals of rest in the slow elevation of the land,
could doubt that the New Zealand terraces have been similarly formed. I
may add, that Dr. Dieffenbach, in his description of the Chatham
Islands (“Geographical Journal” volume 11 pages 202, 205.) (S.W. of New
Zealand), states that it is manifest “that the sea has left many places
bare which were once covered by its waters.”
KING GEORGE’S SOUND.
Public-domain text, read in full here on John Shaqi.
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