Unlike the conspicuous slabs with large compressed fossils
often seen in museums, fossiliferous cherts usually do not make large
fossil exhibits but nevertheless impressive samples if cut and
polished, with life-like three-dimensional
preservation in partially transparent chalcedony, often beautifully
coloured. The preservation of tiny detail even
on the micrometer scale contributes to their
Photograph: Evidence for preservation of tiny detail in transparent
chalcedony. Sporangia of the tree fern Scolecopteris with
clearly seen cells on the surface,
quite uncommon variety with two hairs emerging near the pointed top
of the capsules, (cut off at the lower
sporangium, seen as white spots,) unknown
Lower Permian, Döhlen basin, Saxony, Germany.
Fossiliferous cherts have not received due attention as they
are most often found as pebbles in gravel pits and
fluvial deposits and along rivers but
rarely as outcrops, which makes them unsuitable for stratigraphy.
As an exception to this rule, most of the famous Rhynie chert recovered
hitherto, now stored at museums and universities and not yet fully
investigated, was dug up by
trenching into subcrops of in-situ chert layers . Smaller amounts
have been found scattered in the area, with sizes of a few grams up to
Big chert boulders are rare because the layers break into pieces while being
washed out of the banks and carried along by the river. The width of
the fragments is usually not much larger than the thickness of the chert
layer. The width can even be smaller if the brittle layer had been bent by deformation of the stratum where it is embedded.
The biggest chert boulder from Döhlen
basin is a Lower Permian chert of 31kg with numerous fern frond
fragments, found in a trench in a glazial fluviatile deposit at
Hänichen near Dresden.
The lately increased interest in fossiliferous cherts in Saxony
has been brought about by lucky incidences: (1) first new find of a
"maggot stone" since 1893 by Gert
Müller in 1985 after purposeful search, (2) essay on the old "maggot
stone" finds by M.
1987 , which encouraged the present writer to look for fossiliferous
cherts in a wider area, (3) earthwork and construction pits in
fluviatile deposits with
fossiliferous cherts, since 1991. This interest is held up mainly by the
activity of non-professionals who are fascinated by the
encounter with ancient life forms but don't care
much about stratigraphy. It
manifests itself in lay websites as www.kieseltorf.de and the present one.
It is strongly emphasized that the field work of collecting
cherts differs much from searching for and recovering compression
fossils in sediment rocks where a hammer is a suitable tool.
Fossiliferous chert pebbles and boulders should never be hit with
a hammer. Same as agate pebbles and silicified wood, they should be cut
with special blades, after inspection from outside and choosing a
suitable cutting plane. Luckily, stone cutting with
narrow blades is a widespread trade nowadays.
Judging from experience, anyone who has
carried with him or her a hammer for hours feels the urge to hit
something with it, which can mean the destruction of a unique fossil by
irrecoverably shattering it to pieces. Also, most often details are poorly visible on a fracture face but better on the naturally smoothed surface. The
safest way to
resist the temptation
to shatter a valuable sample is to leave the hammer at home and take a
pickaxe or big chisel along to poke into the ground or into the gravel
In order to show that the danger of irreparable damage is real, a
confession of the venerable A.G. Lyon
examination, by removing small chips with a hammer, ... .
Unfortunately, during the preliminary examination, the block shattered,
but two related pieces of moderate size were recovered ..." . Hence,
the title of the related publication reads "On the fragmentary remains
fact, no chert piece
equalling the shattered one has been found within
half a century, hence the true size and
shape of the fossil have remained obscure.
Incidentally, a fossil closely related to the shattered one serves as
evidence that one can find tiny things by
carefully inspecting the
smooth natural surface of the chert piece: See Rhynie
Chert News 29 , 51 , 71.
H.-J. Weiss 2010
 N.H. Trewin:
History of research on the
the Rhynie area, Aberdeenshire, Scotland.
Trans. Roy. Soc. Edinburgh 94 (2004
for 2003), 285-97.
Barthel: Der Madenstein aus dem Rotliegenden des
in: H. Prescher u.a.: Zeugnisse der
Erdgeschichte Sachsens, Leipzig 1987, S.121.
 A.G. Lyon:
On the fragmentary remains of an organism
referable to the nematophytes, ..., Nematoplexus
rhyniensis gen. et sp. nov.
Trans. Roy. Soc. Edinburgh
LXV (1961-62), 79-87, 2 plates.