David Brookes says (i) that Irish navvies were often concentrated at bridge and tunnel workings in order to avoid fighting between them and the English . The lines "The noise of our tools brave boys, does make the valleys ring / We will drive our piles and bore our holes, by one, by toe, by four" are suggestive of that sort of work. (i) Brookes, David The Railway Navvy: That Despicable Race of Men. (Newton Abbot, David & Charles, 1983) p