v. Cornish Mining. [See quot. 1778. But Jago has ‘wood-tin, costean, an ore of tin in structure like wood,’ f. cos, M.Cornish coid wood + stean tin.] intr. To sink pits down to the rock in order to ascertain the direction of a lode. Usually Costeaning vbl. sb.
1778. W. Pryce, Min. Cornub., Another way of discovering Lodes is by sinking little pits through the loose ground down to the fast or solid country…. This way of seeking the Tinners call Costeening, from Cothas Stean; that is fallen or dropt tin.
1850. Ansted, Elem. Geol., 500. Where their actual presence is doubtful … a series of experiments called in Cornwall ‘costeaning,’ is undertaken with the view of discovering the presence of a vein.
1880. Miss Courtney, W. Cornw. Gloss., Costeening, examining the back of a lode by digging pits.
1884. R. Hunt, British Mining, 502. The pits or shafts sunk are costeaning pits or shafts.
Hence costean pit.
1778. W. Pryce, Min. Cornub., 319. Costean pits are shallow pits to trace or find Tin. Costeaning, ditto.
