I am new to fossil collecting and also to this group. I have left it a bit late to get involved in fossils as I am close to becoming one myself !
I would appreciate any ideas on what the photos show. I have been told that they are not fossils - I had hoped they were some form of encrusting bryozoan. Well there's no harm in hoping !
The rocks were picked up in a local, long disused limestone quarry and there were several pieces showing the same thing so it wasn't uncommon there. Other rocks from the same place show plenty of bits of crinoid stems and shells.
No 1 shows the outer face of the rock. To the top left, and below it, centre of left are two "leaf shaped" areas one slightly green and the other slightly yellow. The rock is covered in tiny holes and also seems to have a very thin coating of something white coloured.
No 2 is an edge view of the rock and shows how thick it is between top and bottom surfaces.
No 3 shows the inner, clean, face of the rock and is cropped to give an enlarged view. As can be seen the surface is well covered in tiny holes. Like the outer surface there is a very thin coating of something on the rock.
No 4 is a view of the top ,outer, surface taken at an angle to try and show the thin coating that is present.
No 5 is cropped to enlarge it more and is of the inner, clean, surface.
No 6 A change is as good as a rest.... this is a different piece of rock with bits of crinoid stem in it this also has lots of the tiny holes in it.
No 7 The same as No6 but rotated 180 degrees. I think the "cigar shaped" piece at the bottom edge is a crinoid stem ???
I have put two small red dots on this photo. Between the dots is a circular pattern of holes. It appears circular rather than random. I found several examples of this and also one eliptical shaped one with slightly larger holes. Any ideas ?
I thought you might like to see these two photos of a Fenestalla Bryozoan. This came from the same place and shows I don't always turn up rubbish !
I only know what it is because someone kindly identified it for me.
It's 3 centimetres across with the less visible part extending it out to 4 centimetres or so total.
Thanks for any suggestions as to what is going on with these rocks.
Just posted another photo.... this has just been taken using LED lighting and shows the layer (of whatever it is) on the rock with all the holes. The thin coating seems to stand out better under an LED light.
Thank you for a very well prepared posting. Nice Fenestella.
The dark "leaf shaped" areas are, I believe, lichen.
The minute holes are due to solution by acid secreted by lichen
Here are a couple of places where the phenomenon is mentioned:
If there is any significance to circular/elliptical patches of holes, they probably reflect particular patches of lichen, which may have been in that spot for some time and happened to be circular. The lichen has since disappeared; it may have been grazed away by molluscs or the rock may have moved such that it came to lay under water or part-buried in soil. That would change the microenvironment, which could lead to the lichen being decomposed.
Thanks Mike, yes the network, net-like fossil is bryozoan. I am interested in the crinoids but cannot see enough detail.I cannot see the location you collected these from - if you can tell us we can approximate an age for your fossils. Struggling to comment on the other specimens, would need to see them in hand specimen. Please visit or post to the Angela Marmont Centre, Identification & Identification Service at the Natural History Museum, London, if you wish them identified further.
All the best,
Thank you for the reply. I am posting some more photos and I hope they are a bit clearer.
The location of the quarry from my GPS is N 54 09.6982 W 003 06.1880
New 4 & New 5 photos is a rock from the same place as the others. I wonder what that stuff is ?
Calcified lichen.... ?
New 6 is just for interest.... it's the long, disused quarry where the rocks came from.
Black lichen covering the rock faces.
Thank you Mike.
I reckon that you are spot on. I followed the links you gave and read up on the effects of lichen.
I also searched and found more info. I never knew what a complicated thing lichen was - amazing.
It's great when a bit of information leads on to gaining knowledge about something else as well.
I am about to post some more photos and I think that "New 7" probably shows the culprit. The rock surfaces in the quarry are covered in this black lichen. In most areas it's a thin layer and in some spots it is quite thick and noticeable. Amazing that the lichen produces acid and drills into the rock .
Thanks again for setting me off on an interesting trail.