The Trenear Mortar Stone - Treasure in a car park!

We already know that Cornwall is pretty special. The sublime scenery, the temperate climate, the precious wildlife . . . the pasties. But in the Bronze Age it was something else that drove the economy. The tin and cooper found close to the surface and running through the veins of Cornwall’s bedrock. And the unique Trenear Mortar Stone is evidence of this early industry.

Treasure in a Car Park

The most amazing objects can be found in the most unlikely places. Of course, the ‘amazing’ part is all a matter of personal perception. After all, the Trenear Mortar Stone is just a slab of granite.

But its history and rarity makes it a treasure. This unassuming chunk of granite is the only known prehistoric ore-grinding mortar in Britain.

The stone was first surveyed by archaeologist Sandy Gerrard, who made a plan of it in 2004 and had it scheduled. It lies in the parish of Wendron, beside the beautiful River Cober, in the car park of Poldark Mine.

Sandy told me:

“It is probably unique and for this reason doubts concerning its identity can be entertained. However given the lack of rock art in the south west and the proximity of the rock to one of the richest alluvial deposits in Cornwall a mortar stone interpretation seems good.”

This large earthfast slab has at least 17 circular or oval shaped hollows worn into its upper surface. These hollows are thought to have been used as ore-grinding mortars at some point in ancient history. Christian Boulton in his book Five Million Tides suggests that it is almost certainly a relic from the Bronze Age.

Fortunately the Trenear Mortar Stone is well preserved. It was until recently partly buried, which protected the rich environmental and archaeological information for the elements. However, given how little information there is available about it, further study is definitely needed.

Bedrock Mortars

Bedrock mortars are a very tangible connection to our ancient ancestors. They are usually a series of man-made circular or oval depressions in a rock outcrop or naturally occurring earthfast slab of stone. Bedrock mortars are found across the United States as well as in the Middle East. The Raqefet Cave rock mortars in Israel were used to prepare malt for beer some 13,000 years ago, while sites in California were used to grind acorns and other food stuffs at least 7000 to 8000 years ago.

Bedrock mortars are also known as Gossip Stones referring to the close communal activity undertaken to produce them.

Interestingly when Sandy Gerrard was completing his survey of the site he recalls that he was approached by a South African tourist.

[He]told me he had seen a similar stone being used to crush gold . . . in Africa.

The Crushing of Tin

Some say it was the Sumerians, from modern-day Iraq, who discovered that adding a small amount of tin to molten copper produced the wonderful and useful new alloy – bronze. Whatever the case that invaluable knowledge found its way to Cornwall, where all the ingredients necessary for this alchemy were in plentiful supply.

The area around Trenear is particularly rich in tin and it has been harvested there from the earliest times.
It is amazing i think that the innocent looking hollows in the Trenear Mortar Stone were made by man, probably thousands of years ago. And unlike the cup-marked stone at the Tregiffian Barrow these marks are not meant to be decorative. They are a sign of industry.

All the hollows are found along the southern, lower edge of the rock and they vary in size and depth. The largest is roughly 22cm long, 20cm wide and 10cm deep. The inner surface of all of the hollows is worn smooth as a result of the repeated action of stone on stone during the crushing process.

Unlike the bedrock mortars discussed above, these hollows were almost certainly formed by human hands crushing and pounding tin ore from a nearby alluvial streamwork, not food stuff. This hand working of the ore is thought to have been carried out in Cornwall before stamping machinery was invented during the medieval period.

No one can ever know exactly when the Trenear Mortar Stone was in use, by whom and how long for, but it is without doubt a simple but truly marvellous relic hiding in plain sight. So why not pay it a visit?