Basset and Grylls Mine inrush, 1858

On 24 August 1858 the floor of an old shaft at Porkellis, filled to three or four fathoms with dressing-floor waste and covered by half an acre of tin slimes, gave way. Slime and water poured down through the 24 fathom crosscut into the deep workings, where some fifty men ran for their lives; seven were buried. The ground fell in over about 2,000 square fathoms and the bodies could not be recovered.

Cause

Men working in the back of the 12 fathom level on the south lode cut too close to the sollar, or false floor, of an old shaft that had been filled with slime and waste from the dressing floors; it gave way under the weight above.

What happened

The slime ran through the 24 fathom crosscut into the deeper levels on the north lodes, where about fifty men were working. A rush of air put out their lights and the roar was heard at the surface; the men came up the shaft 'like a swarm of bees'. The slime rose to the 24 fathom level, filling 41 fathoms of the 65-fathom sump shaft. Three of the dead were shaftsmen and the rest worked in the deeper western levels. Ten or twelve dressing frames went down with the ground. Upwards of 2,000 people gathered at the mine.

Rescue & recovery

Two other men feared lost were found safe before a rescue shaft was begun. Digging for the bodies was judged too dangerous, as the slightest disturbance sent tons of rubbish down the chasm, and they were left under the slime; the miners refused to work.

What's uncertain

Points where sources disagree or the record could not be settled; both accounts are kept. All open questions in the archive.

• Six men and one boy died. (disputed) ²

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• On 24 August 1858 an inrush of slime at the Porkellis (Basset and Grylls) mine killed seven. ^1,2
• Men working too close to the floor of an old shaft filled with dressing waste weakened it, and slime and water poured into the workings. ^1,2
• The ground fell in over about 2,000 square fathoms, leaving a hole some 54 by 36 metres and 9 metres deep. ^1,2
• Six men and one boy died. (disputed) ²

Related terminology

Mining terms this disaster is structurally linked to, with the nature of the relationship.

• Crosscut (contextual relationship)
  Named twice in this record, first in the summary: “…slimes, gave way. Slime and water poured down through the 24 fathom crosscut into the deep workings, where some fifty men ran for their lives;…”
• Dressing Floor (contextual relationship)
  Named twice in this record, first in the summary: “…of an old shaft at Porkellis, filled to three or four fathoms with dressing-floor waste and covered by half an acre of tin slimes, gave way. Slime and…”
• Fathom (contextual relationship)
  Named 7 times in this record, first in the summary: “…1858 the floor of an old shaft at Porkellis, filled to three or four fathoms with dressing-floor waste and covered by half an acre of tin slimes,…”
• Lode (contextual relationship)
  Named twice in this record, first in the cause: “Men working in the back of the 12 fathom level on the south lode cut too close to the sollar, or false floor, of an old shaft that…”
• Sump (contextual relationship)
  Named in this record’s narrative: “…rose to the 24 fathom level, filling 41 fathoms of the 65-fathom sump shaft. Three of the dead were shaftsmen and the rest worked in the…”

Sources

1. (secondary) NMRS: Porkellis Mine Slime Inrush, Helston, 1858 — Northern Mine Research Society
2. (observational) Explore Cornwall: Basset and Grylls — Explore Cornwall

Record created: 11 October 2026 · Last researched: 11 October 2026