RootsChat.Com

Think you are too early.
Ancestry has a collection UK, Registers of Births, Marriages and Deaths at Sea, 1844-1890 that a relation's birth & death appear in 1877 en-route to Queensland. He also appears in Australia, Death Index, 1787-1985.
For later maritime deaths of crew there has sometimes been an approximate location for the death but no record of when or where the burial at sea was conducted.
https://discovery.nationalarchives.gov.uk/details/r/C3196
https://discovery.nationalarchives.gov.uk/details/r/C3197
For Richard Elphick there is no death record on Ancestry or Findmypast.

No. It would be thousands of pages and images long for all the Union's in Ireland published in different years/decades for the 32 counties of Ireland (took 17 years). There were some 160 odd Unions but 301 volumes. Volumes were identified in the various archives, digitised and indexed by Eneclann Ltd, OMS Services and The National Library of Ireland originally, back in 2003. Is now name indexed on Ancestry and Findmypast, as well as AAI (Findmypast says there are over 2.9 million records).
Download the pages you need. You can browse the images using the thumbnail image viewers on Findmypast & Ancestry page back or forward. You could do it manually for a Parish but wouldn't have the name index to go with them. Move on to the re-valuations/revisions etc.

https://www.irish-genealogy-toolkit.com/griffiths-valuation.html
https://www.johngrenham.com/browse/retrieve_text.php?text_contentid=67
https://www.findmypast.co.uk/articles/griffiths-valuation---explanation-of-terms

Names for Parishes can be downloaded from https://www.failteromhat.com/griffiths.php

Family tree on Family Search (would need to all be verified) has lots of information and gives Mr. Greer as a Robert Alexander Greer

See especially the Alert notes on Mary Anna Emerson https://www.familysearch.org/en/tree/person/details/KCTN-7QV and the research Notes to the right on both her and Robert Alexander Greer. "Current living family members believe her husband's name was Robert Alexander Greer"

There are no Irish sources for Mary or her children and she is stated as thought to have been born County Londonderry reason: From arrival ship manifest, family biography in notes and private family research.

Sources commence with the passenger list where she is listed as Anne Greer [indexed as Green] aged 50 a Baker [dittoed from above, but perhaps occupation should be none] from Ireland, destination Maryland https://www.familysearch.org/ark:/61903/1:1:QK6L-GTD3?lang=en
and on the next page James 19 & Richd 14, Farmers with destination Ohio.

On the FS tree at least I see no evidence of where in Ireland any were from from the census records or Naturalization linked. Mary Anna Emerson is Anne Greer in all the Knox, Ohio Land Tax records, Anna Greer in 1830 census.

AnthonyMark

Just for your interest Marriage #1.
Marriage 27 Sep 1885 of Thomas Mansell, aged 22, Bachelor (Labourer) of 34 McClure Street, Belfast & Ellen Jane Collins, aged 22, Spinster (Stitcher) of 43 Lake Street, Belfast. Fathers Matthew Mansell (Builder) + John Collins (Cloth-passer).
https://irishgenealogy.ie/files/civil/marriage_returns/marriages_1885/10872/5970674.pdf

Thomas Maunsell obtained Ellen Jane Collins affections by sending a faked letter stating that her former lover had been killed in the wars. After marrying Mansell he had left her, whereabouts unknown [maybe Birkenhead area where was born, but parents had moved to Belfast when only 4]; was allegedly presumed dead until his return 1891. [ref newspapers on her prosecution]

Bigimous marriage #2 to her former sweetheart, under assumed names. 25 Mar 1887 of Thomas Douglas, aged 26, Bachelor (Labourer) of 8 Malt Street, Belfast & Mary FLOOD, aged 23, Spinster (Machinist) of 29 Excise Street, Belfast. Fathers = Thomas Douglas (Labourer) & Thomas Flood (Carpenter).
Husband also used pseudonym, was correctly Thomas Douglas Harvey.
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1887/10789/5934783.pdf

4 Feb 1891 CHARGE OF BIGAMY. Ellen Jane Harvey, alias Mansell, arrested at 41 Osborne Street by Sgt. Cunningham of Antrim Rd. Magistrates asked for a remand to get the certificates of the two Belfast marriages contracted by the prisoner, maiden name Ellen J Collins.
13 Feb 1891 Recorder's Court, Belfast.
Ellen Jane Maunsell indicted with having committed bigamy by marrying Thomas Douglas Harvey in Drew Memorial Church, Belfast, on 24 Mar 1887, her former husband, Thomas Maunsell, to whom she was united on 27 Sep 1885, in St Anne's, being still alive.

https://search.findmypast.co.uk/bna/viewarticle?id=bl/0000434/18910204/249&stringtohighlight=ellen
https://search.findmypast.co.uk/bna/viewarticle?id=bl/0000434/18910206/169
https://search.findmypast.co.uk/bna/viewarticle?id=bl/0000098/18910206/013&stringtohighlight=bigamy
https://search.findmypast.co.uk/bna/viewarticle?id=BL/0001631/18910214/074/0003
https://search.findmypast.co.uk/bna/viewarticle?id=bl/0000038/18910214/032&stringtohighlight=harvey

Belfast Evening Telegraph, Saturday, February 14, 1891. "BELFAST RECORDER’S COURT. His Honour Henry Fitzgibbon, Q.C., Recorder of Belfast, and the County Judge for Antrim, resumed the business of the Recorder’s Court, in the Municipal Buildings, at eleven o’clock this forenoon. Mr. William Carson, J.P., Clerk of the Peace for the City, was in attendance. BIGAMY. Ellen J. Maunsell was indicated that on the 27th Sept., 1885, at the parish of St. Ann’s, Belfast, did marry one Thomas Maunsell, and that the said Ellen J. Maunsell, alias Harvey, afterwards, and whilst she was so married, on 24th March, 1887, at the Drew Memorial Church, Belfast, feloniously and unlawfully did marry one Thomas Douglas Harvey, her former husband being then still alive. Mr. M'Erlean, on behalf of the prisoner, pleaded guilty. His Honour allowed the prisoner to stand out on her own recognisances to come up for judgement at ten days’ notice."
I did not find a report of what she was fined or how long a custodial sentence was 10 days later.

1901 census with her husband from the bigimous marriage and two sons.
https://www.census.nationalarchives.ie/pages/1901/Antrim/St__George_s_Ward_Belfast/Colchester_Street/955022/
1911 boarding with another family saying they had been married for 24 years (1887).
https://www.census.nationalarchives.ie/pages/1911/Down/Victoria__part_of_/Cuba_Street/224823/
Younger son William John Harvey's birth registered as legitimate child of Thomas Douglas Harvey & Ellen nee Collins.
https://irishgenealogy.ie/files/civil/birth_returns/births_1895/02208/1834025.pdf

No additional annotation on EITHER of the quarterly return marriages sent to Dublin per the above pdf's and both indexed under those names on GRONI (equivalent to Local GRO copy in England, each marriage indexed from one of the pair of original bound church marriage ledger copies, one sent & retained in the Registration District when filled & stored with the original local birth & death ledgers) as that was all the North had after Irish Partition 1922.

Ellen Jane Harvey is buried with her bigimous husband Thomas Douglas Harvey in Dundonald Cemetery, they appeared to have lived happily together once the case was over. One son died WW1, the other in the Belfast Blitz WW2 serving with the Naval Reserves.

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1st husband Thomas Mansell 1901 census said was married to a Minnie, but they NEVER actually married and had no children, from their GRO deaths you would think they had been. Would have been bigimous I guess as his 1885 marriage was still valid.
https://www.census.nationalarchives.ie/pages/1901/Antrim/St__George_s_Ward_Belfast/Matilda_Street/956484/
Death 13 May 1901 at 247 Matilda Street of Marian Mansell, aged 38, Married (Wife of Thomas Mansell, Plumber) of Cerebral Haemorrhage. Registered 13 May 1901 by Thos Mansell, Widower of deceased, present at death.
Death 12 Nov 1901 at 101 Argyle Street of Thomas Mansell, aged 38, Widower (Labourer) suddenly, from Heart Disease.
Marian was interred in Public ground of the City Cemetery, Thomas in same cemetery but with relatives in plot adjacent to his parent's headstone.

Perhaps your are not replying to B J Peak or Hugh Sutherland in particular. Neither have been online for 10 years and their only posts were in this thread if check their profile but they may still get a notification.