The GRO references for ten Years of Births
registered in England and Wales (Jan 1841 - Dec 1851)
for people with the surname.

For the majority of births the father's surname of Smithies was recorded and the mother's surname did not appear in the GRO registers of the time.
However, where a child was born to an unmarried mother the father's name was not published on the birth certificate. So only the single mother's name was provided in the GRO registers.
To make this clear, a — appears in the mother's name column.