The growth of industry resulted in the arrival of large numbers of workers from Ireland who moved into the factories and mines in the 1830s and 1840s. Many were seasonal workers employed as navvies on the construction of docks, canals and then railways. An estimated 60–70 per cent of colliers in Lanarkshire were Irish by the 1840s. The arrivals intensified with the Potato famine of 1845. By the census of 1841, 126,321, or 4.6 per cent of Scotland's population, had been born in Ireland and many more were of Irish descent. Most were concentrated in the west of Scotland, and in Glasgow there were 44,000 people who were born in Ireland, 16 per cent of the city's population. Most Irish immigrants, about three quarters, were Catholic, leading to a major cultural and religious change in Scotland, but a quarter were Protestant, eventually bringing with them institutions like the Orange Order and intensifying a sectarian divide in the major cities.