Interesting Stones

Greyfriars and the Leper Chapel are the last surviving buildings of ancient Dunwich. Their walls are full of interesting stone types.

There are blocks of imported and shaped Jurassic limestone from Caen in Normandy and the Peterborough area. These were used for masonry, such as in arcading and window frames.

The walls are mostly made of rubble, particularly locally-sourced flint cobbles from the beach and nearby gravel pits, but also boulders of far-travelled material brought from northern England and Scotland by ice sheets and from Scotland and Scandinavia as ballast in the bilges of Mediaeval ships. 

Interesting stones are also found in the walls of St James's Church, built in the 1820s from the rubble of ruined buildings.

Here are some pictures. They link the  ancient city to its landscape and its overseas trading hinterland.

 

A small boulder of Swedish Kristianstad flint - presumably a block of ship's ballast.

Two iron-stained flint cobbles, probably sourced from the Crag, 

a local marine deposit about 2 million years old.

A split boulder of dolerite, a type of igneous rock. The rounded contours of its exterior

suggests it is likely to have been rounded by wave action. It may well be an example

 of ballast from Scandinavia or northern Britain.    

A boulder of pink granite. It could be from north-east Scotland or southern Sweden.

A boulder of chalk, a limestone of Cretaceous age, perhaps 70 to 90 million years old.
Chalk outcrops in parts of East Anglia and could have been transported to the 

Dunwich area by glacial ice. It could also be an example of ballast from the coast 

of northern Germany.

A block of sandstone, probably the Old Red Sandstone formed in deserts of Devonian 

age, perhaps 400 million years ago. This distinctive rock type outcrops in 

northeast Scotland and the Orkney islands.

A boulder of augen gneiss, a distinctive metamorphic rock with clots of whiteish 

feldspar mineral which are said to resemble eyes. This specimen could be from 

Scotland or Scandinavia.

Blocks of mudstone which originated from the Harwich area, Essex. This mudstone 

was deposited in a sub-tropical sea in the Eocene period, perhaps 52 million years ago. 

There is a large amount of it in the walls of the Leper Chapel.

A slab of volcanic lava. Disc-shaped blocks of this lava were imported from the

Rhineland (Germany) in Mediaeval times for use as quern stones for grinding corn.  

Their fragments are often found in East Anglian church walls.

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