I am trying to identify the parents of my great-grandfather Thomas Jones (born 5 March 1870 in Dowlais, Merthyr Tyfdil, which ties up with all his census entries from 1881 onwards.) I know their names but cannot track them down before or after the birth of one of their only known child.
What I know and how
His father was Thomas Jones, 'Agent', and his mother was Elizabeth (formerly Hughes) -- all this information from his birth certificate (using a date of birth found in the 1939 Register, and verifying with the Merthy Tydfil register ofice that there was no other Thomas Jones born in Dowlais on that date.
By the time of my great-grandfather's marriage in 1893, his father was recorded as a deceased Engine Driver (which probably means a stationery engine at a pit).
Looking for siblings
Searching the GRO indices for other children with the surname Jones and others maiden name Hughes born before and after Thomas isn't a feasible proposition -- Jones and Hughes were very common names in the South Wales coal fields.
Looking at the first census after he was born:
My assumption is that if my Thomas was born in March 1870, his age and birth place in the 1871 census would be given quite accurately.
In the 1871 census there are only 6 candidates born in Dowlais between 1869 and 1871; there are a further 9 born in Merthyr Tydfil. None of them have one or both correct parent(s)...
... except for a Thomas Jones aged 1 in the household of William Harries born abt 1811 and his wife Jane born abt 1816 both in Carmarthenshire. Alongside their unmarried children born 1849 to 1863 (all in Dowlais or Merthyr Tydfil) is an Elizabeth Jones a widow aged 28 (so born abt 1842/1843) in Dowlais and Thomas Jones aged 1 born Dowlais:
(There are no other candidates born Glamorgan with a correct parent and a birthplace that isn't too specific to be an option).
Elizabeth Jones is shown as the granddaugher of William Harries and Jane, which is where this particular difficulty starts.
Can she really be the grandaughter of the head of household?
I have traced Willian and Jane (and their children) back through the censuses to 1851 -- their ages and place of birth are consistent (1811 Carmarthenshire for him and 1818/1820 Carmarthenshire for her.) I've also correlated the childrens' births via the GRO indices and determined that Jane's surname is Matthews. There is a marriage of William Harries to Jane Matthews in 1846Q2 Merthyr Tydfil. I haven't found either of them conclusively in 1841.
However, if Elizabeth Jones was born 1843, her parents would have been born circa 1827 at the latest, so she cannot possibly be the granddaughter of William and Jane -- either as a result of their current marriage or any potential previous marriages (they did marry unusually late in life, so may have had previous marriages).
What other possibilities exist?
It's possible that she's the illegitimate daughter of Jane, but there isn't an Elizabeth Matthews born to mother with the maiden name Matthews in Merthyr Tydfil between 1841 and 1845. She might also be a legitimate daughter of Jane by a previous marriage, but checking for an Elizabeth born to a mother with the MMN Matthews is an impossible task (especially as the GRO indices won't let you search without a surname).
It's possible that she's the daughter of William by a first marriage, and two possibilities born 1841-1845 in Merthyr Tydfil: Elizabeth Harris 1842S (MMN Roberts) and Elizabeth Harris 1842D (MMN Jones) which I have not yet tracked forward to confirm or eliminate them.
Why is she shown as a grand-daughter when she clearly cannot be one? What other relationship might she have to the family with which she is living? How can I confirm any hypotheses about the relationship?