Beagle Expedition (1831-1836); Geology -- South America; Volcanoes
Behind Hobart Town there is a small quarry of a hard travertin, the
lower strata of which abound with distinct impressions of leaves. Mr.
Robert Brown has had the kindness to look at my specimens, and he
informed me that there are four or five kinds, none of which he
recognises as belonging to existing species. The most remarkable leaf
is palmate, like that of a fan- palm, and no plant having leaves of
this structure has hitherto been discovered in Van Diemen’s Land. The
other leaves do not resemble the most usual form of the Eucalyptus (of
which tribe the existing forests are chiefly composed), nor do they
resemble that class of exceptions to the common form of the leaves of
the Eucalyptus, which occur in this island. The travertin containing
this remnant of a lost vegetation, is of a pale yellow colour, hard,
and in parts even crystalline; but not compact, and is everywhere
penetrated by minute, tortuous, cylindrical pores. It contains a very
few pebbles of quartz, and occasionally layers of chalcedonic nodules,
like those of chert in our Greensand. From the pureness of this
calcareous rock, it has been searched for in other places, but has
never been found. From this circumstance, and from the character of the
deposit, it was probably formed by a calcareous spring entering a small
pool or narrow creek. The strata have subsequently been tilted and
fissured; and the surface has been covered by a singular mass, with
which, also, a large fissure has been filled up, formed of balls of
trap embedded in a mixture of wacke and a white, earthy,
alumino-calcareous substance. Hence it would appear, as if a volcanic
eruption had taken place on the borders of the pool, in which the
calcareous matter was depositing, and had broken it up and drained it.
ELEVATION OF THE LAND.
Public-domain text, read in full here on John Shaqi.
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