John Joly tracking Oldhamia

John Joly (1857-1933) was an Irish professor of geology, trained as engineer, who made important contributions to geology, mineralogy, geophysics, tectonics, geochronology, but also optics, chemistry, photography, mechanics and laboratory equipment. He discovered his love for geology in 1880, during a field trip into the hills south of Dublin, where he collected various specimens of minerals and fossils. Seventeen years later he managed to convince the Trinity College that he, due his experience and expertise in the field, was the right man for the, at the time, vacant position as geology professor.

During a walk in County Wicklow in the winter of 1984 he observed how ice crystals had formed an intricate pattern in the muddy soil. The pattern reminded him of Oldhamia, a trace fossil of unknown origin he had collected in Cambrian (541-485 million years ago) rocks at Bray Head.

Could it be that these presumed fossils were in fact of inorganic nature? 

 "Elements of Geology" by C. Lyell (1871)

Joly tried to replicate the patterns in the laboratory by freezing various samples of soil and mud, and succeeded to reproduce a pattern resembling an ichnofossi - Oldhamia radiata. However he failed to reproduce other similar ichnofossils with a more complex pattern, like Oldhamia antiqua. He blamed his failure in part to problems to exactly reproduce the grain size distribution of the sediments preserving the traces.

Later Joyle realized some other problems in his hypothesis with the inorganic origin of the Oldhamia fossils. O. radiata was found in the field always as depression, O. antiqua in relief, probably resulting from the relationship between the bedding plane and the mechanism by which they were produced. 

An inorganic mechanism, like freezing, would probably show no such preferences. Today it is also known that the Cambrian sediments where Oldhamia fossils can be found were deposited in deep water, not as Joly imagined along shores or tidal flats, where the mud could freeze.

 
Bibliography:

JACKSON, P.N.W. (2011): History of Ichnology: John Joly (1857-1933) on Oldhamia: Poetic and Scientific Observations. Ichnos 18(4): 209-212