Essex Rock & Mineral Society Field Trip
Shropshire Weekend 10th & 11th May 2003
by Iain Brown

I recently accessed the ERMS web-site and was interested to find the field trip report for the above weekend. Having joined the trip as a supernumerary being a kindred spirit from the Bath Geological Society I was motivated by Roger‘s comments about sharing to burst into print mainly as a thank you to ERMS and David Turner in particular for letting me attend. Finding a Trilobite has long been an ambition of mine which I‘ve now fulfilled. It should be also noted that the following is my personal recollection of the weekend extracted from an all to fallible memory. I’m also new to fossil collecting so the identifications and technical stuff will not be of the highest order.

The first picture is from the first site on the first day - Overtons Rough. As you can see it’s not a particularly good specimen but it’s special to me as it’s the first Trilobite I’ve ever found. The rocks in which it was found were loose crumbly wet shales.

Another feature of note is apparent distortion which I assume is due to folding activity sometime in the 460 odd million years it’s been lying around waiting for somebody to find it. Could be that it’s such a poor specimen that this is what it looks like and no tectonic stuff has happened. (Note 1)

As for what it is when I showed it to Bob Kennedy he reeled off a string of words within which I believe I heard the name Calymene. Looking in the Natural History Museums British Palaeozoic Fossils yields the prefix Flexi or Platy for Calymene in the Ordovician. Unfortunately the specimen is so poor it is hard to make a closer identification. If forced, I’d say Flexicalymene caractaci.

The second site on the first day was Deltons Wood and proved the most productive for me for an unusual reason. The first site in the locality fossil bearing rocks were very hard and I managed to split the handle of the hammer I was using as my enthusiasm outweighed my skill. Hammerless we then moved on to the second site where I was forced to scavenge around in the loose stuff for finds. Fortunately quite a high proportion of the rocks I picked up had fragments of Trilobites in them. These were usually fragments of the complete fossil perhaps discarded by earlier collectors. Here’s a few.

This is the thorax and tail piece (pygidium) of, I believe, Ogygiocarella (Oggy for short).

This is an example of the top part of an Oggy.

It shows the glabella and about 6 segments of the thorax. The glabella is the central raised part of the Trilobite head (note:- the specimen is the negative half of the fossil). The complete head shield of a Trilobite is called the cephalon. My specimen hasn’t got the full cephalon as it is lacking bits called cheeks which lie either side of the glabella.

(Specimen about 25mm across at the widest)

Another species of Trilobite that was common was Onnia and shown in the next two pictures.

In this view, the specimen is tiny but complete. Most collectors would have thrown it back as too small but as this was my first time on a Trilobite hunt I was happy with anything.

(Size about 6mm across)

Here is a bigger example and though also complete it is partially obscured by the head shield of another.

If you look closely at this picture you may just make out the genal spine which Onnia has extending from head shield down parallel to the thorax. Also the curious rows of ‘dots’ or pits on the head shield which in life were some kind of sensory device.

(Size about 20mm across)

The second day started at Acton Scott which represented a different environment back in the Ordovician. The other sites on the first day where what Bob called ‘life assemblages’ which means the animals actually lived (and died) locally. Acton Scott was a calcareous mudstone and represented a site where various animal parts would congregate through wave action or gravity after death. This meant the chances of a complete Trilobite was small however this was offset by the chance of finding other types of fossil.

This picture shows a head shield of (again) Calymene with other fossils around it. Also thanks again to David Turner who loaned me his heavy duty hammer and chisel with which I extracted this fossil.

The above picture is the reverse of the same piece of rock and shows an abundance of Ordovician brachiopods with about four types in evidence. Also of interest is the five pointed star just below the centre line on the right which I assume is a crinoid fragment.

The second site on the second day and also the last of the weekend was in the River Onny. Bob told us the colour of the rocks to look out for and the sound they made when struck by a hammer. However despite this instruction I was unable to find anything so no pictures I’m afraid. An rather unproductive end to a very enjoyable weekend in darkest Shropshire hunting Trilobites.

Pictures & Text by Iain Brown (2003)

As an aside the pictures have been re-engineered from those supplied, the colours are false due partially to; incorrect "white balance" in the first instance, and reworking to provide an acceptable image within the constraints of website space. (RC.)

Note 1. Distortion of fossils, a difficult subject but the original compaction and lithifaction of the sediments is perhaps the mechanism for distortion in many cases. One could look for other evidence such as distortion following the same pattern as bedding plane folding in the shales (if any) which could hint at tectonic influence. If one is serious about deciding the causes of distortion, petrological examination in thin section will yield additional useful information. (RC)
(Back)

Very many thanks to Iain Brown for sharing his experiences with us all.

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