Throughout the previous year the railways had been extending through the English border country and into Scotland. A third of the navvies were Irish, a third Scots, and a third English: that was the beginning of the trouble - easy-going Roman Catholic Irish, Presbyterian Scots, and impartially belligerent English. - Terry Coleman’s ‘Railway Navvies’

Nothing "easy going" about Roman Catholicism (Far to many strictures: You can't do this, you can't do that. You must eat this you can't eat that on certain days. You must do this, you must do that - all bound up in anything against the diktat of the Pope, the Bishop or the Priest is a mortal sin that will send you to hell). Presbyterianism while strict in observance has far fewer such strictures. Wonder why after describing the others in terms of religion Coleman then describes the English Navvies as he does - surely they would have mostly been Church of ENgland (The most laid back religion in the world, born as it was out of convenience).

Hidden in all the cut'n'paste verbiage the real reason the Irish emigrants were met with hostility not only in Liverpool, Glasgow, Boston, Chicago and New York is given:

their one genuine grievance (the fact that the Irishmen would work for less pay and so tended to bring down wages)