1) Some kind of mill stone, the precise meaning is uncertain.
In documents which relate to corn mills there are not infrequent references to blue stones, e.g. 1746 Thomas Horn for a pair of Blue Stones, Whitley. A few years previously, in 1740, the diarist Arthur Jessop noted There hath been a vast great Mob ... who I hear pulled up several Mills were there was Bluestones, New Mill. The editor’s comments on this second reference were added to by Dr Hemingway of Leeds University’s Geological Department who offered three possible interpretations, none of them completely satisfactory in his own words. He did however say that freshly-quarried sandstones can be off-white to grey-blue and that a rock known as ‘Bluestones’ occurred near Keighley, although he considered this to be unsuitable for mill-stones. It may be, of course, that ‘blue stones’ had become a sort of generic, inspired by awareness of the high-quality blue stones quarried in Germany. In 1751, a man was reported to have bought some blew stone and gone about selling it, but this is likely to have been copper sulphate.