your previous topic on the Dyer family stated that the marriage was in a registry office - see :
Re: Joseph DYER from Emo (reply #8)
I presume this is the extracted version of the marriage from FamilySearch :
Groom: John Horgan
Bride: Eliza Dyer
Marriage date: 20 Aug 1861
Marriage place: Coolbanagher, Queens Co.
Groom's father: Jeremiah Horgan
Bride's father: Joseph Dyer
Ref.: p259 ln67
see :
https://familysearch.org/pal:/MM9.1.1/FGCC-QJFand the corresponding BMD Index reference (the year and page number and general area match the extracted record) :
Name: Eliza Dyer
Registration district: Mountmellick
Event type: Marriage
Year: 1861
Volume: 8 / Page: 259
the fact that this is included in the Civil BMD Index means that it was a non-Catholic or Registry Office marriage.
You can use the Index references to order a research cert, which will give you a few more details on the marriage, from the GRO by post. See :
Ordering Certs from GRO Roscommon Details included on a Marriage CertS.