SNAKESTONES OFFER A SLIVER OF INSIGHT INTO HISTORY

Friday, February 1, 2008

Ammonite found by the author in 2003 on a walk with the geological group. Picture by Helen Slade.

NATURE NOTES
By Helen Slade
of the IW Natural History and Archaeological Society
IT IS not only living plants and animals which occupy the minds of members of the IW Natural History and Archaeological Society.
As well as members who examine the past life of human beings through the study of archaeological remains, there are those with a particular interest in the study of extinct life forms.
The Natural History Museum describes palaeontology as the study of prehistoric life in the geological past, using fossils. We happen to live on an island where this is a rewarding area of study, as demonstrated a couple of weeks ago in this newspaper with the discovery of a huge ammonite fossil at Whale Chine (CP, 11/01/08).
In fact, I have experienced at first hand the excitement of finding a fairly large ammonite, although not of quite such enormous proportions. I was fortunate to discover the ammonite pictured right on a walk with the society’s geological group. It caused great excitement because it appeared to have been found in a layer of rock in which it was unusual to find this particular type of ammonite.
Ammonite fossils in general are common and widespread but individual species or sub-species often survived for periods of 2 million years or less. Although that may sound a long time, geologically, of course, it is not, so it is possible for ammonite fossils to assist with dating rock formations in different places which may contain the same fossil species. This is helpful to scientists producing geological maps and surveys, or when prospecting for oil or other minerals.
Because ammonites have been so intensively studied, many different species have been identified and named, but their actual lifestyle must continue to be the subject of a great deal of educated guesswork based on knowledge of their closest living relatives.
As cephalopods, ammonites are related to living molluscs such as the cuttlefish, octopus and squid families and in appearance are, superficially at least, very like the modern nautilus. The shells of ammonites — and modern nautiluses — are made of a mineral called aragonite, or mother-of-pearl but the fossils you find will not normally show any remnants of the actual shell. The shell would have been composed of a number of segments, which increased with the age of the ammonite, but it has usually dissolved away, the segments having first been filled with sediments. This produces the three-dimensional type of fossil pictured here and like the one found at Whale Chine. Other fossils may simply be crushed flat and left as impressions in the rock.
The familiar spiral shape of ammonites has lent itself to architecture and jewellery and their abundance as fossils has contributed to the development of myths. In Whitby, North Yorkshire, there is a story that the town was plagued by snakes until the Abbess, St Hilda, turned them all into stone. The nature of the local geology allowed the fossils to be carved with snake’s heads, resulting in them commonly being called snakestones in England. In India, ammonites are a traditional wedding gift from the bride’s family to the bridegroom, as a symbol of the supreme Hindu god, Vishnu.
I am indebted to a marvellous book published by the Natural History Museum for these delightful snippets and for a host of other very readable information about all aspects of ammonites. 'My’ ammonite has been taken to the Natural History Museum for identification and may perhaps one day help to shed further light on the study of these pretty fossils.

Suggested further reading: Ammonites by Neale Monks and Philip Palmer, published by the Natural History Museum (2002), ISBN 056509169-7.

SNAKESTONES OFFER A SLIVER OF INSIGHT INTO HISTORY

Weather

Subscribe