PS Regarding the earlier discussion of soldiers enlisting in Abergavenny, which of course provided men for the Monmouthshire Regiment as well as the Borderers, I've just found this site which may be usefull for future research of this type. This excellent site lists and includes backgroud details of all the men on Abergavenny's Memorial.
http://historypoints.org/index.php?page=abergavenny-war-memorial-fww

In fact this is just one section within a website to War Memorials all across Wales. The site has an excellent search engine, eg enter "Marshall" and it lists several Memorials which include this name.

1911 Census, Castle ford, Yorks.

Albert Parsons, Head, 42, Married 22 years (=1889) Coal Miner Hewer, b. Glos. Forest of Dean
Elizabeth , Wife, 42, b. Glos. Forest of Dean
Vida A.J . Booth ,Daur, 22 , b. Glos. Forest of Dean
Albert J. Parsons, Son, 17, ? Cleaner Glass Works, b. Yorks. Castleford
William H. Parsons, Son, 13, School, b. Yorks, Castleford
Frederick Parsons, 11, Son, 11, School, B. Yorks, Castleford
Nora M. Parsons, Daur, 4, b. Yorks, Castleford
Archie Booth, Son-in-law, 21, Driver below gound, b. Yorks, Castleford
John Marshall, Nephew, 27, Labourer, ?? Company, b. Glos, Newtown

Albert’s marriage:-

Record_ID: 21050
Entry_Number: 160
Year: 1888
Month: May
Day: 20
Grooms_Surname: PARSONS
Grooms_Forenames: Albert
Grooms_Age: 20
Groom_Condition: Bachelor
Grooms_Occupation: Coal miner
Grooms_Residence: Ruardean Hill
Grooms_Fathers_Surname: Parsons
Grooms_Fathers_Forenames: Benjamin
Grooms_Fathers_Occupation: Coal miner deceased
Brides_Surname: SEVERNE
Brides_Forenames: Elizabeth
Brides_Age: 21
Brides_Condition: Spinster
Brides_Occupation: [not stated]
Brides_Residence: Ruardean Hill
Brides_Fathers_Surname: Severne
Brides_Fathers_Forenames: Charles
Brides_Fathers_Occupation: Coal miner
Licence_or_Banns: Banns
Date_of_Banns: [not stated]
Signature_or_Mark: Both sign
Witness_1: William Wilce
Witness_2: Mark of Lortitia Tippins
Other_Witnesses:
Officiating_Minister: William Barker Vicar
Event: Marriage
Memoranda:
Notes:
Register_Reference: P109 IN 1/8
Page_Number: 80
Parish_Chapel: Drybrook

The link with the Marshall family?? Was Agnes Elizabeth’s sister?

Record_ID 3179
Entry_Number 315
Year 1880
Month Dec
Day 28
Grooms_Surname MARSHALL
Grooms_Forenames William
Grooms_Age 29
Groom_Condition Bachelor
Grooms_Occupation Labourer
Grooms_Residence Cinderford
Grooms_Fathers_Surname Marshall
Grooms_Fathers_Forenames William
Grooms_Fathers_Occupation Labourer
Brides_Surname SEVERN
Brides_Forenames Agnes Martha
Brides_Age 20
Brides_Condition Spinster
Brides_Occupation [not stated]
Brides_Residence Cinderford
Brides_Fathers_Surname Severn
Brides_Fathers_Forenames Cha[rle]s
Brides_Fathers_Occupation Labourer
Licence_or_Banns Banns
Date_of_Banns
Signature_or_Mark Both mark
Witness_1 Mark of James Brooks
Witness_2 Mark of Maria Brooks
Other_Witnesses
Officiating_Minister W[illia]m Lynes Vicar
Event Marriage
Memoranda
Notes
Register_Reference P85/1 IN 1/5
Page_Number 158
Parish_Chapel Cinderford St John

And John’s baptism:-

Record_ID 130010
Entry_Number 759
Year 1883
Month Nov
Day 18
Parents_Surname MARSHALL
Child_Forenames John
Fathers_Forenames W[illia]m
Mothers_Forenames Agnes
Mothers_Surname
Residence New Town East Dean
Occupation Labourer
Officiating_Minister C A Borrer Rector
Event Baptism
Memoranda
Notes
Register_Reference AG68/6
Page_Number 95
Parish_Chapel Hope Mansell

The obvious problem is that this all relates to an area just north of Cinderford. I can’t see a link with this John Marshall and Clearwell.

1891 census, Yorkley

MARSHALL - John 37, Clara 34,
children, Reuben 15, William 13, Bessie 11, Harry 9, Albert 7, Tom 5, Minnie 3 and Fred 1 month

John has 6 sons, and none have his name on census returns - unless they are known by their middle name(s)???

-

Glosbdm

John MARSHALL married Clara BLUNT at the Forest of Dean Register Office 1878

Albert John MARSHALL - birth registered 1883 - Forest of Dean, Monmouth Coleford

-----

By searching for Marriages etc at Clearwell for Marshall (this appears the only MARSHALL at Clearwell)

we have

21 April 1913

Albert MARSHALL aged 27, Bachelor, Miner - residence, Ellwood, Clearwell (?is he known as John)

father: John MARSHALL (deceased)

married Elizabeth Blanche JONES

witnesses: John JONES and Minnie MARSHALL

etc etc

- on GlosBDM can't see any MARSHALL/JONES births registered at all after 1913

http://www.rootsweb.ancestry.com/~engcots/ClearwellPhotos.html

Forest of Dean WW1 Servicemen
Transcript Details

Record_ID: 3501
Year: _
Surname: MARSHALL
Forename: John
Rank: Private
Regiment: _
Service_Number: _
Residence: Clearwell
Notes_1: _
Notes_2: _
Newspaper: _
Date_Published: _
Image: _
Soundex: M624

Do you know whether Clearwell Memorial is commemorating all those who served, or "only" those who gave their lives ?

The CWGC site lists over 260+ "J Marshall"s, at least 60 of these are definitely Johns, who died during the War. Have you searched their database, a long job I know but sometimes their records include details of nextofkin which are very helpfull. ?
I suspect this entry MAY be the same man you mention, Abergavenny being in the SW Borderers' "catchment" area.
http://www.drillhalls.org/TownAbergavenny.htm

MARSHALL, JOHN
Rank:Private
Service No:8924
Date of Death:21/08/1915
Regiment/Service:South Wales Borderers
2nd Bn.
Panel ReferencePanel 80 to 84 or 219 and 220.
MemorialHELLES MEMORIAL
Additional Information:

http://www.cwgc.org/find-war-dead/casualty/688331/MARSHALL,%20JOHN

Helles suggests the Gallipoli / Dardanelles campaign.

??????

I've tried searching the BNA and Welsh Newspapers websites but to no avail, unfortunately "Marshall" supplies many thousands of newspaper hits relating to Field-Marshalls and the like...

Most WW1 mentions of Clearwell relate to Pte George Miles, who was awarded the V.C.
???
http://www.glosters.org/milesvc.htm

-----------------

Searching this site's PRs for Marshall in Clearwell gives;
Record_ID: 31225
Entry_Number: 271
Year: 1913
Month: Apr
Day: 21
Grooms_Surname: MARSHALL
Grooms_Forenames: Albert
Grooms_Age: 27
Groom_Condition: Bachelor
Grooms_Occupation: Miner
Grooms_Residence: Ellwood Clearwell
Grooms_Fathers_Surname: Marshall
Grooms_Fathers_Forenames: John
Grooms_Fathers_Occupation: Deceased
Brides_Surname: JONES
Brides_Forenames: Elizabeth Blanche
Brides_Age: 22
Brides_Condition: Spinster
Brides_Occupation: [not stated]
Brides_Residence: Ellwood Clearwell
Brides_Fathers_Surname: Jones
Brides_Fathers_Forenames: Richard
Brides_Fathers_Occupation: Carpenter
Licence_or_Banns: Banns
Date_of_Banns: [not stated]
Signature_or_Mark: Both sign
Witness_1: John Jones
Witness_2: Minnie Marshall
Other_Witnesses:
Officiating_Minister: William Robinson
Event: Marriage
Memoranda:
Notes:
Register_Reference: P88 IN 1/5
Page_Number: 136
Parish_Chapel: Clearwell
Soundex_Groom: M624
Soundex_Bride: J520

I wonder if tracing this family might produce another younger John Marshall ?.

I also find this Record that MIGHT possibly be connected to this quest ?

Record_ID: 84055
Entry_Number: 266
Year: 1918
Month: Jun
Day: 24
Grooms_Surname: MARSHALL
Grooms_Forenames: Albert John
Grooms_Age: 25
Groom_Condition: Bachelor
Grooms_Occupation: Serving in HM Forces
Grooms_Residence: not stated
Grooms_Fathers_Surname: Marshall
Grooms_Fathers_Forenames: John Henry
Grooms_Fathers_Occupation: Caretaker
Brides_Surname: TAYLOR
Brides_Forenames: Mabel Florence Ellen
Brides_Age: 24
Brides_Condition: Spinster
Brides_Occupation:
Brides_Residence: Tregarth Hartpury
Brides_Fathers_Surname: Taylor
Brides_Fathers_Forenames: Walter Frederick
Brides_Fathers_Occupation: Retired postman
Licence_or_Banns: Licence
Date_of_Banns:
Signature_or_Mark: both sign
Witness_1: Walter Frederick Taylor
Witness_2: Florence Bessie Watkins
Other_Witnesses: E H Taylor
Officiating_Minister: Nathan Jones Vicar
Event: Marriage
Memoranda:
Notes:
Register_Reference: P165 IN 1/18
Page_Number: 133
Parish_Chapel: Hartpury
Soundex_Groom: M624
Soundex_Bride: T460

???