Something strange slithered here

This beautiful little packhorse bridge carries the footpath over Thorsgill beck beside Egglestone abbey in Teesdale. It probably dates from the 17th. century and countless feet must have passed over it since it was built. But when you stand on the top there is evidence of something else that slithered over its stones, around 300 million years ago.

One of the capstones carries this strange serpentine marking. Some long-extinct invertebrate left its trail when it wriggled across the tropical sea floor back in the Carboniferous, before the sediment turned to limestone.

Visit to a tropical coral reef

Bollihope, just south of Frosterley in Weardale, can be a bleak place at this time of year. Acres of brown heather and withered bracken, with a few small conifer plantations. But if you follow some of the burns that flow down into the bottom of the valley you soon find yourself standing on a tropical coral reef, albeit a 325 million year-old one.

This is the subject of Thursday's Guardian Country Diary

This is the rock known as Frosterley marble, which is not a true marble at all but a fine grained, dark limestone full of fossil Dibunophyllum bipartitum coral. In this slab you can see one almost complete piece of the horn-shaped coral in longitudinal section and two pieces in transverse section. The contrast between the fossil and the stone matrix becomes much greater when you make it wet or polish the surface. 

The state of preservation of the coral structure is astonishing.  This particular specimen is embedded in a slab that must have once been a small waterfall until the burn changed course. It has been worn smooth by flowing water.

Medieval craftsmen spent months cutting and polishing the rock by hand to achieve a smooth, marble like black surface that revealed the fossils in this detail. Their work can be seen in pillars of the Chapel of the Nine Altars in Durham cathedral and in the pillars in the Bishops' Palace at Auckland castle in Bishop Auckland, as well as in smaller objects like the font in Frosterley church. 

It's also in the flagstones on the floor of the bar of the Black Bull pub in Frosterley.

Frosterley marble floor decoration in the Laing Art Gallery, Newcastle-upon-Tyne

Rock of Ages

The Durham coast isn’t a top destination for fossil hunters, who find richer pickings further south under the crumbling cliffs around Whitby, but occasionally interesting fossils do turn up on our beaches. I found one has week, on Blast beach just south of Seaham, which gave a tantalising glimpse of how the landscape might have looked three hundred million years ago.

Blast beach was formerly a site for dumping colliery waste but in recent years the magnificent Turning the Tide project has made great strides in restoring this coastline to its former, pre-industrial glory. There are still large boulders on the beach that were transported with colliery debris and it was when I split one of these that I found the remains of a plant that had been embedded in the rock for three hundred million years.   The compressed, jointed stems, now turned to stone, belonged to a giant horsetail.If you double-click for a larger image you can see that there are two reasonably intact compressed fossil stems here - one running at an 11 'o'clock to five o'clock angle and the other running eight o'clock to two o'clock.

Back in the Carboniferous, when the coal measures and the land mass that is now Britain was nearer the equator, these strange plants formed tropical, forests in swamps that would have been home to early amphibians and giant dragonflies.

Horsestails still exist today, as 'living fossils', but are a pale shadow of their extinct ancestors. Gardeners are familiar with the field horsetail, which is a troublesome weed but only grows about a foot tall. Today specimens of the great horsetail, the largest horsetail species that grows in damp places along this coast, reach a height of about five feet. Judging by the width of the fragment of fossil stem that I found, this long-extinct plant must have been at least four times as tall. Larger fossils that have been found indicate that these ancient plants sometimes grew to a height of sixty feet or more. 

A quick Trip back to the Jurassic

The North Yorkshire coast, southwards from Staithes to Port Mulgrave, is famous for the range and quality of Jurassic (200-145 mya) fossils that are constantly eroded from its crumbling cliffs. These are a few of the many fossils I saw during a visit last week.

An ammonite....

...... another ammonite ......

..... another one ...

....... and even more ammonites. There are hundreds of them, which makes this a popular area with fossil collectors.

These ........

..... and this are (I think) brachiopods.

Fossilised oyster shells......

..... and scallops Pseudopecten ...

.... which are the most distinctive bivalve mollusc fossils along this stretch of coast.

Fossilised U-shaped burrows of a shrimp-like animal called Rhizocorallium.

A narrow seam of jet - fossilised remains of a tree similar to the present-day monkey puzzle.

.... and finally, there's always a strong possibility that you can strike gold here. Unfortunately it's fool's gold, iron pyrites, but when it encrusts fossils like this one it is rather beautiful.

A Lost World

( These fossil corals are in the drystone wall near the Packhorse Bridge that you can see in the bottom photo at http://cabinetofcuriosities-greenfingers.blogspot.com/2009/08/scotch-argus-butterflies-south-of.html)

Hard to believe at first sight, but the limestone ridges in Ravenstonedale in Cumbria that the kestrel (in the bottom photo – click to enlarge) was hunting over were once the beds of warm shallow seas somewhere near the equator back in the Carboniferous period, over 280 million years ago. The evidence is there to see in the form of fossils in the drystone walls, built from limestone boulders, that criss-cross the valley that Scandal Beck has carved out from the limestone. The fossils in the stones are corals called Siphonodendron, whose tentacles would have swayed in ocean currents. At the time when these animals were alive small early reptiles were beginning to evolve and giant dragonflies hunted through steamy swamps. The first flowers, that are such a conspicuous feature of these limestone grasslands today, would not put in an appearance for another 150 million years.