Geology Corner

Geology Corner

One of our Palace 800 events was to have been some fascinating geological tours of the Palace by geologists Dr Douglas Robinson and Chris King, telling the stories behind the stones at the Palace.

As we can’t run the tours, we thought our website viewers might enjoy a monthly instalment instead!

The Bishops Palace buildings and the Gardens display rock types from the local area that tell a story of the region’s 200 million year history from c. 380 to c. 175 million years ago (Ma). These rocks record the region’s movement from southern tropical latitudes across the equator into northern temperate latitudes. Over the next few months this Geology Corner will explore these different rock types and tell you where to find them in the buildings or gardens. But first the origin of the Wells springs. 

The ancient springs – but how ancient are they? In the Heart of Wells for 800 years are the Bishop’s Palace gardens in which the Wells Springs arise, and which have been called Ancient Springs – but just how ancient are they? The springs flow at an average rate of some 18,000 m3 (~ 4 million gallons) per day. Dye tracing has shown that the springs are fed by an underground passage or natural series of linked caves running almost due east from the Palace gardens beneath the Tor Woods area to their main source at stream sinks on the southern side of Beacon Hill some 9 km east of the city. 

The bubbling St Andrew’s spring, less than 250 m southeast from St Andrew’s well in the gardens, just across Tor St on the edge of Tor Woods, are rocks of Triassic age (c. 250 - 200 Ma). The sediments that formed these rocks were deposited when the area was part of a large arid continent at the latitude of present day North Africa. These rocks have evidence of fossil soils bearing rootlets, but such fossil soil features have not been found any where else in rocks of this age in the Mendip area. These rare fossil soils from the arid Triassic desert environment must mean that there was a regular supply of fresh water forming an oasis in the ancient desert, suggesting that springs like today’s were running some 200 million years ago!

The image above is of Triassic rocks some 200 Million years old at Tor Woods, with fossil soil horizon containing vertical cream coloured tube-like structures formed by fossil plant rootlets.