Thanks to all those readers who contacted us to point out that the picture of a rock on Portland that appeared in the previous issue of NSS was not in fact the 100-tonne boulder being transported to Compton Verney.

The picture showed Pulpit Rock, the landmark at Portland Bill, which must be at least 50 times heavier than the block actually moved.

Ben Murray, the manager at Hanson Bath & Portland\'s Coombefield Quarry, from which the 100-tonne block was extracted, kindly sent us the picture here of the actual block leaving the quarry and making its way to Compton Verney in Warwickshire.

Hanson Bath & Portland donated the massive piece of Portland to John Frankland, taking part in the Summer Arts Programme at the 18th century Compton Verney mansion. The theme of the exhibition is passage and routes and the progress of the stone from Portland to the exhibition was all part of the art.

At Compton Verney the block was up-ended on the front lawn to stand 4.5m high. The theme of the exhibition was developed by climber Johnny Dawes discovering routes to climb the rock so that visitors could interact with the exhibit by clambering over it.

The boulder was the biggest single piece of stone ever to leave Portland, but it was not actually the 100 tonnes that the publicity people said it was - more like 80 tonnes, says Bath & Portland\'s Matt Gould.

And, as we pointed out last time, neither was it actually the famous Portland limestone responsible for the character of so many buildings in London and elsewhere. It is a piece of the cap stone that lays over the Portland stone itself and is usually blasted off and used for aggregate.

The enormous boulder cannot stay in the front garden of Compton Verney once the exhibition is over because it only has temporary planning permission, although as it cost the artist £10,000 to transport it to the exhibition it is not quite clear where it will go afterwards. Matt Gould had a suggestion, although he added: It might make your eyes water! Ouch!