1) No definition available
Few examples of this term have been noted in reference works and the only quotation in the OED is for 1881 where it is explained as ‘the bottom of the shaft’. It has a much longer history than that: 1574 when they dryve owte of the eye, Sheffield
1690 parte of pitt eye coale getting, Farnley. The same term was used by miners of ironstone and lead: 1630 1 pickman or hewer will require 1 carrier from him to the neyt or eye pit, there one winds it up, Derbyshire. In fact, it was an alternative word for ‘pit’ in ironstone-mining: 1576 one Pitt or Myne called One eye of Iron Stone, Farnley. The inference is likely to be that in shallow pits the ‘eye’ marked the place where daylight gave way to darkness, although few of the references are detailed enough for that to be evident: 1706 framed the fallen pitt eye, Farnley
1714 from the old pitt eye, Shibden. At times it is as though the ‘eye’ was the whole shaft. It should be quite distinct from the ‘pit mouth’ which was the pit head but the two are on occasion used confusingly as apparent synonyms: 1754 to lay, dispose and place on such part of the said demised premises as shall be near to the mouth or eye of the pit, Beeston
1806 about eight yards from the eye or mouth of the pit, Horsforth. Of course in drift mines, those with a horizontal gallery, it would be more difficult to draw a distinction between the eye and the mouth.