Thomas or Jones?!

[Janice Jones]

Hi, I hope someone can help me to stop going round in circles!
My Mother - Miriam Kathleen Collins (Nee Whines) 19/9/1933 - 12/7/2015
Her Mother - Gwen Griffiths - 1911-1990 (Co of Glamorgan but lived middle years in London)
Gwen's Parents - William Griffiths (1872-1943)and Jane Lewis (1878-1948)
William's Father - David Griffiths (1845-)(I think I'm ok to here)
I think David Married Mary - Pontypridd 1870
Then then big trouble starts for me as I think I've narrowed it down to a choice of 2 Mary's, one is a Thomas (Pontypridd Sept 187011a 457)  the other is a Jones(Pontypridd Sept 1870 11a 438)! In Wales!!

I've tried checking with the census, but I'm really struggling now to narrow it down more

Any ideas - or maybe I've gone wrong already?

Thanks in anticipation

Jan

[CaroleW]

A copy of William Griffiths 1872 birth cert will give his mothers maiden name

[Janice Jones]

Thank you.