For most of us, a rockery is a small agglomeration of natural-looking stones at the far end of a garden, and an opportunity to grow delicate alpine flowers and succulents. That’s a rather 20th-century notion, perhaps a little quaint. And it is dramatically at variance with Joseph Paxton’s grand picturesque vision at Chatsworth, where from 1842 he created a craggy wonderland designed to transport visitors – in the imagination at least – to wild Yorkshire moorland, or perhaps even as far as the Alps, whence the 6th Duke of Devonshire (together with Paxton, as his head gardener) had
