This one?
Conkwell Cave No. 1 (near Bradford on Avon) - 22 August 1973
Source – Bristol Evening Post – 23 August 1973
PUPIL TRAPPED FOR TWO HOURS UNDER ROCK
A West schoolboy was recovering today from a two hour ordeal in a disused quarry trapped beneath a huge rock the size of a wardrobe.
Anthony Comer (18), of Dane Rise, Winsley, near Bradford-on Avon, had to be freed by firemen from a shaft in the disused Conkwell quarry at Winsley.
He was attended by Bath casualty officer Dr. Roger Snook and taken to the Royal United Hospital, Bath for observation on a sprained ankle. He was allowed home today.
The incident happened last night as Anthony, an experienced caver, and his friend John Gibbs (17) of St. Nicholas Close, Winsley, decided to explore the old shafts.
The two boys clambered through the maze of tunnels separately. As Anthony went to search for a rock for a schoolmaster friend he was trapped by a rockfall.
His father Mr. Allan Comer said today: “He was properly dressed and they alerted people outside the quarry that they were going in.
“The two boys were separated in case anything happened.
“A large piece of stone came out of the roof, but Anthony was aware of it and jumped out of the way.
“But it trapped his boot and he fell over, spraining his ankle.
The rock was too big to move, so John, a young soldier home on leave from the Army, went to get help from people living nearby. Mr. Comer was alerted.
He went into the cave to talk to his son. They were planning to lever the rock away when police and firemen arrived.
After a long battle, Anthony was freed by firemen using hydraulic jacks and levers.
Anthony a sixth former at Fitzmaurice Grammar School, Bradford-on-Avon has been caving for four years.
But Mr. Comer today warned inexperience people against exploring the old quarry, which supplied the limestone for the Limpley Stoke viaduct over the River Avon.
“Anyone venturing into any quarry who is not experienced should only go in with experienced people,” he said.