The "petrefact" collection of the Supreme Forestry Advisor of Saxony, HEINRICH COTTA (1763-1844), is regarded as one of the most important collections of its time. That part alone which had been transferred to Berlin after his death is made up of about 5000 fossils of plants and creatures. Nowadays, samples from his collection are kept at the Museum fuer Naturkunde der Humboldt-Universitaet Berlin (Inst. of Palaeontology), also at the Museum fuer Naturkunde Chemnitz, Bergakademie Freiberg, Staatliche Naturhistorische Sammlungen Dresden, and British Museum of Natural History. Unfortunately, a few samples got lost.

The historical background and a survey of the Berlin part of the collection are given in [1]. The survey mentions fossiliferous cherts from the Rotliegend shales at Ruedigsdorf near Chemnitz. In 2004 I got the opportunity to inspect and partly record the samples assigned to Ruedigsdorf. (Thanks are due to M. BARTHEL and S. SCHULTKA for their kind support.)

5 drawers with 180 samples have been inspected and identified as 99 cherts with and without fossils, 73 pieces of petrified wood, and 8 Psaronius trunk fragments. Expecting to see the typical dark brown laminated chert blocks with Sigillaria patterns as I knew them from Ruedigsdorf, I was surprised to find out that 83(!) of the samples were non-typical but otherwise familiar, with their rounded shapes, adhering sandstone, colored diffusion zones, squeezed Paronius and well-preserved Scolecopteris pinnules! These features give rise to the suspicion, and after thorough inspection make it seem highly probable, that the corresponding samples are not from Ruedigsdorf at all but from the well-known type locality of Scolecopteris elegans near Kleinnaundorf. Here are a few arguments related to this hypothesis.

Pro:

HEINRICH COTTA lived at Tharandt, which is not far from the Doehlen basin with the Kleinnaundorf locality, and one part of its collection goes under the heading "Rotliegend des Doehlener Beckens". One should assume that he was able to tell the Kleinnaundorf samples from the Ruedigsdorf ones but there is a possible source of confusion: The catalogue of the collection was not prepared during his lifetime but after his death by his son CARL BERNHARD COTTA (1808-1879). The slovenly labelling may be attributed to the erroneous view that Rotliegend is a continuous subsoil stratum throughout Saxony, or it may simply have been done in a hurry.

Among the most probably mislabelled samples there is one which is certainly so: a fluoritized Dadoxylon as it is known from Chemnitz-Hilbersdorf only, labelled Ruedigsdorf. A minority of the chert and petrified wood samples labelled Ruedigsdorf seem to be really from there. They are not rounded and often merge into fine-grained tuff. They look like freshly broken from solid rock, which apparently could be done in the quarries at Ruedigsdorf around 1800.

Contra:

The above thoughts blame BERNHARD COTTA, the honourable professor at Freiberg, for the blunder. One would not expect this, considering his highly esteemed work published 1832. He should have known the difference between the Ruedigsdorf and Kleinnaundorf fossils. Should he really? Can the answer be found in his writings?

Or else it might turn out that the Kleinnaundorf-type cherts were really found at Ruedigsdorf then since, of course, one cannot exclude this possibility only because they are not found there now. Perhaps this question can be answered by geologists familiar with the site.

Means:

One could apply standard techniques to determine chemical composition and age for comparison but this would be cumbersome and expensive. Before doing tests one should try simpler means. For example, the labels should be checked against BERNHARD COTTA's original catalogue. Also comparing the samples from the Ruedigsdorf and Doehlen parts of H. COTTA's collection can be helpful, even without the unlikely coincidence of finding two fitting halves. In some way or other, the search will go on.

Supplement:

In summer 2005, COTTA's collection has been thoroughly inspected. Although I did not find the "fitting halves", some other interesting things were found out. For example, it seems that the registry number of every sample can give a clue concerning the place where it was found. The related results have been published in [2].

photographs: H.SAHM/Dresden, text & photographs: R.KRETZSCHMAR/Chemnitz