The South Moor witherite deposit was discovered in the workings of the Morrison Pit (formerly Holmside and South Moor Collieries Ltd) in 1931 when a drift was made from the Hutton Seam engine plane to prospect a faulted area and reached the deposit 2miles south of the then Morrison North Pit. The vein (not seam) was developed over 2,500ft. There is the rest of the information in Geology of the Northern Pennine Orefield by Dunham. These collieries including Craghead, South Moor, Ushaw Moor, New Brancepeth were all on the edge of the orefield and the Witherite and Barytes deposits were all found mostly as oreshoots along promonent faultlines.