Agate and fossils from watery habitat (4)
Picture: Silicified swamp matter including fungi
and early land
plants, with perfectly straight horizontal interface between former
watery liquids.
Width of the level 7.6mm.
This
picture together with this headline may seem incom-
prehensible: Where
are the fossils and why is it called agate ? Admittedly, most agates do
not show straight lines, which are really cut plane faces, but if there
is a straight line in chalzedony, the whole may justly be called agate.
However, it must be mentioned that most of the fossils seen in
exhibitions
or offered for sale are in no way related to agates. There are
only a few fossil-bearing locations world-wide where small fossils are
well preserved in chalzedony from silicified swamp water, eventually
with
small agates
close by or even inside. The most famous location of such
type is near Rhynie, Aberdeenshire, where this picture comes from.
This sample from the Lower Devonian may remind the observer of the fact
that those were the times when plants
had ventured onto dry land not long before, in the Upper Silurian,
probably in
symbiosis with fungi,
according to results of recent research [1]. Lots of
thin fungus hyphae are present in this sample, recognized in the black
layer only by their thick coatings of bluish chalcedony.
Highly
peculiar is the perfectly straight horizontal line bordering
the
black layer, which is liable
to be misinterpreted as a former liquid surface. It is remarkable that
the hyphae cross the
border as if a liquid surface had never been there, which indicates
that, instead of a surface, there had been a level interface
between a dark watery suspension,
possibly of dead microbes, and the
water. This suspension must have been sufficiently liquid to form a
perfectly
plane interface, with the coated hyphae sticking through. (The aspect
suggests a heavy suspension. In case the dark suspension would have been
lighter than water, the picture should be turned upside down.)
What looks like a sea monster in the upper half
of the picture is a
squeezed specimen of the early land plant Aglaophyton
(former Rhynia major),
silicified while lying in the swamp water.
What looks like an eye is a fungus organ known as chlamydospore. The
xylem strand of the plant is preserved
while other tissue is not. Another xylem cross-section, with several
tracheids with black fill, is seen near
the lower edge.
Sample:
Rh14/3.2 (2005) 1.9kg, obtained from Barron.
[1] T.N.Taylor, M. Krings, E.L. Taylor: Fossil Fungi,
Elsevier 2015.
H.-J. Weiss
2019
 |
 |
145 |