William Turner's 1793 Essay on the Terra Ponderosa and the source of the Type Material of Witherite

A recently rediscovered manuscript of William Turner's 1793 essay on ‘Terra Ponderosa’ provides a remarkable contemporary account addressing confusion over the type locality for the newly described mineral witherite, the key question being whether or not witherite was known from Alston Moor at the time. Turner's essay corroborates the reaffirmation by Cotterell (2022) that the type material came from Anglezarke, near Chorley in Lancashire, as first stated by Watt 1790, rather than Alston Moor. Turner's manuscript provides a description of unpublished experiments conducted in 1782 by William Irvine, Professor of Chemistry at Glasgow University, on ‘native aerated Terra Ponderosa’ from Leadhills, later misattributed in chemistry texts as having been found by Withering. It also indicates that John Smeaton, formerly a co-receiver of the Greenwich Hospital (holder of the mineral rights) for the Alston Moor mines, had supplied the type material studied by Withering, his earlier association with Alston Moor possibly contributing to the initial misattribution of the type locality.