Assuming I've found the same "Ancestry" tree referred to by Tree Tective - I, personally, would NOT put any great faith in the information contained in it. There are no birth or baptism dates given, and therefore I can only assume that this family is based on the 1851 and 1871 census returns and the information then inserted into the tree for whatever reason, as I can't see much forward evidence.
My advice would be to look for baptismal records for St Dogmaels, and as Mariah is said to originate from St Dogmaels, perhaps the marriage records as well.