Oh, really? I love that. It is par for the course with many pre-C20 works. Not only Gaskell but lots of ther C19th novelists do it. The gothic novelist Ann Radcliffe used to jam quotes in to show off her erudition and make people take her seriously as a woman writer (this was in the 1790s).
Epigraphs can be really witty, funny, ironic, or interesting. Totally geeky, but the three epigraphs which start off Maynard Mack's biography of Pope make me go all chilly (yes, I know them by heart):
'He was a poet and hated the approximate.' - Rilke
'Never say you know the last word about any human heart.'
'I! fuge! sed tutior domi.' - Martial
<slinks off to get a life, perhaps several, on reflection>