Cookworthy discovered china clay at Tregonning Hill where it was known as “moorstone”. He was visiting the Great Work Mine and noticed that the miners were repairing furnaces with clay. He found that this clay was good for making porcelain and leased several clay pits on the Hill. The clay was shipped from Porthleven to Plymouth, where he lived. By December 1766 he had set up a small factory in which he manufactured items as a trial.
The clay from Tregonning Hill was not top quality, as it contained dark specks of mica. Better quality deposits were found at St Stephen’s, near St Austell, and this replaced that imported from Tregonning Hill.
Because of a slump in the china clay industry the Tregonning workings were abandoned in 1839. In 1851, the setts were leased to William Browne of St Austell who opened new works called Leeds, close to Cookworthy's original operations. Cooksworthy's original setts were leased to William Lobb, also from St Austell.
1863 a new pit, Tresowes Moor, was opened by Henry Wheeler Higman, from St Austell.
1871 Leeds sett was relinquished and passed on to William Harvey of Hayle.1876 Leeds was being worked by William Argall of Breage and John Toy of Helston, having sublet the property from William Harvey.
1886 Argall expanded his china clay empire and took over Higman's Tresowes Hill works. 1889 he took the other Tresowes setts. More clay reserves were discovered but Argall retired from the china clay business in 1889 and his setts were put up for sale. Most of the setts, including Wheal Grey, were taken up by John Lovering and Company of St Austell and one sett was taken up by a consortium which included James M. Holman (of the engineering company), Francis Harvey (of the Hayle Foundry) and F. H. Thomas (manager of Dolcoath Mine).
Wendron Mining District