Imagine the surprise of the Roman soldier who, many hundreds of years ago, filled his leather water-bottle from a little stream by the River Croco in Middlewich. For on tasting the liquid, he found that it was a rich brine, as salty as sea water. This of course was of great importance to the Romans, who valued salt as a flavouring, preservative, and even as a means to payment to troops; sal is the origin of our word salary.
Through the ages, water had percolated down through the marl rocks, dissolving salt from the ancient deposits, and in places emerging as brine streams in the low-lying valleys of the Dane and Weaver. The exploitation of the natural brine streams continued through Roman, medieval and more recent times, but as levels dropped, brine pits were dug throughout the mid-Cheshire area.
But the main sources lay deep below the surface, on the wet rock head of the salt beds. These lay up to 150 metres below ground, and extracting this brine by mine-shafts was an unpredictable and hazardous job.
The first sign that a shaft was about to reach the brine was a change in the texture of the marl rock. The diggers would strike a granulated layer – shaggy marl, or “horse-beans.” Below the horse-beans lay a hard marlstone layer – the “flagg” – and this had to be pierced, before the brine could be accessed.
This was the dangerous moment; the volume and pressure of the brine were unknown, but a considerable hydrostatic head had built up over the centuries. It became the practice to line the shaft with iron cylinders, the lowest cylinder having an iron bottom with two sealed 10cm bore-holes. When this was in place, a boring rod would be inserted to pierce the flagg and release the brine.
This often had an explosive effect; a deep hollow boom and a gush of released brine surging up the pipes. A contemporary account:
“…..all being ready, the engineer and an assistant gave three blows to one hole, which knocked it through, and the brine entered, making a report like a cannon; then giving three blows to the other hole, they struck it through likewise, and in the midst of the brine, as it was filling the sump, they rushed out amongst it, as well as they could, and getting into the bucket, escaped up the shaft, closely followed by the rising brine…..” (Dickinson, 1882)
The power of the surge in some shafts overcame the workers, who struggled to escape with their lives. Major Townshend of Wincham reported that two 13cm holes released brine which rose 22 metres up a 1.5 metre-wide shaft in 8 minutes.
Eventually a “stuffing box” with stop valves controlled the flow. There remained the possibility that the new brine source would in fact poach liquid from other salt-workings, and this remained a problem in an area honeycombed with shafts.
Why was the underground brine stream called Roaring Meg? This goes back to Civil War days. In 1646, Parliamentary forces besieged Goodrich Castle in Herefordshire for many months. In desperation, they cast a huge cannon, or trench mortar, “Roaring Meg,” which flung 90kg cannonballs filled with gunpowder into the walls of the castle, shattering its defences, and quickly bringing about its surrender. Were Northwich salt-workers among the soldiers, who on their return compared the dull boom of surging brine to the report of the massive cannon?