The prevalence of pneumoconiosis varies from one coalfield to another. The present investigation arose from the observation that coal-miners' lungs from west Cumberland appeared much less black and had less coal in them than lungs from South Wales coal-miners.
Dust analyses were carried out on 33 lungs of coal workers from Cumberland which had been examined histologically and graded according to the classification of Belt and King (1945). No case of massive fibrosis (grade 4) occurred and this condition seems to be rare or absent in Cumberland. Compared with South Wales coal-miners' lungs, each histological grade of simple pneumoconiosis was on an average associated with less coal dust and more rock dust in Cumberland, and silicosis due to rock work in coal-mines appeared to be relatively more frequent.