Mary Alderson
born April 1814–April 1815
  in York, Yorkshire
died very roughly 1884

1841 census: living with husband and children at East Lee, Easington. Age is 25–29, not born in county.

1851 census: living with husband and children in Waldridge. Age is 36 and place of birth is the city of York.

Daughter Mary was born when she was about 17. I suppose that 'Alderson' was Mary sr's maiden name and that Mary jr was born out of wedlock, though it is possible that she was the product of a short-lived marriage to a man called 'Alderson'.