
You have gotten the juices flowing on this matter of research that you raised Rosinish.
The simple matter is to take the easy road, and say that John was born 24 May 1858 in Paisley Refrenshire (and leave it at that, because there is good background on that date). His bother Thomas was born 24 May 1856 in Coatbridge, Lankashire. Note that the dates have a similarity.
We have struggled with the Amos name, and while we have good feelings on it as far as San Francisco goes - it was not easy to find this Irishwoman in Scotland.
However, along comes JAP

a while back that came up with a clinker. No, it wasn't just that the dates duplicated each other but that there were other complicating factors.
To put it in a nutshell, he came up with evidence that seems to indicate that Mary Amos did in fact have two children: John and Thomas. They had birthdays that were similar to those previously reported, but a little different.
This is what JAP found:
At the ScotlandsPeople site,
http://www.scotlandspeople.gov.uk, he found:
Statutory Births, Ref 573/01 0232; 1858, Births in the Parish of High Church in the Burgh of Paisley.
(Name) MCGEOCH, John
(Born) 1858, May seventeenth, 5h 0m am, 14 Broomland Street, Paisley
(Sex) M
(Father) John McGeoch, Dealer in Cattle
(Mother) Mary McGeoch, maiden name Amos
(Informant) Mary Torbett, Her X Mark, Aunt, Present (at birth); (signed) Louis Stream(?), Registrar, Witness (i.e. to Mary's Mark) (Registered) 1858 May 20th, At Paisley, Louis Stream(?), Registrar
Note that Aunt Mary Torbett signed with her mark. As JAP noted, "perhaps she could not read and so had no idea what name the Registrar had recorded; also, perhaps she had a strong Irish accent (and the Registrar might have had a strong Scots accent!)."
This is a very interesting development in that "McGeoch" was never known to have existed prior to this. It could very well be that she assumed the name McGaffigan or Gaffigan, never letting her children know of the true name. But we just don't know, at this point.
The problem is that I have lost track of JAP in my way from this board.
Good Luck, Rosinish
There may be some of the Gaffigan Clan that would like to bury this development in the darkest part of the closet, but there may be some that would wish to track it down - if possible.