The poet suggests that people were jostling for places in a very crowded train. In order to compete with the Clyde steamers, the Glasgow, Paisley & Greenock Railway offered standing-room only fourth class travel for just 0.27 pence per mile.

Reference:
Stuart Hylton, The Grand Experiment: The Birth of the Railway Age 1820-45 (Hersham, Ian Allen, 2007) p94