CLARK(E), Hatfield, early 19th century
PLEASE NOTE: When this question was asked the amount of information available online was very restricted and the only census available (on a CD) was the 1881 census. The answer given below should be carefully checked using the additional information now readily available online.
Denise Pianta (guidop @t one.net.au) of Sydney Australia is the great great grand daughter of Mahala Clark who was baptised in Hatfield in 1825, the daughter of John and Sarah Clarke. She has not been able to identify their marriage and as a result is looking for ways of establishing their identity.
When a comparatively uncommon name such as George Seabrook can cause some head scratching - see Right Name, Wrong Body - it is clear that there are no easy answers for common names such as John Clarke. It is almost certain that there were more than 50 people of that name living in Hertfordshire at any one time. You may well find it useful to look at the web pages on births and baptisms.
I did a quick check and quickly found Mahala Clark and her siblings using the IGI at familysearch - they were: Elizabeth CLARK: 21 Feb 1816; Mary Ann CLARK: 20 Sep 1818; Eliza CLARKE: 20 Aug 1820; Isabella CLARK: 12 May 1822; Ambrose CLARKE: May 1823; Mahala CLARK: 10 Jul 1825; Louisa CLARK: 18 Feb 1827. This would suggest a wedding date of 1815 or earlier. There is no "obvious" wedding in the IGI or the Vital Records Index and while I have not checked the Allen Index at HALS it only contains a few extra marriages that are not recorded elsewhere. There could be many reasons why the wedding is missing ranging from an indexing error (ii.e. it is in the register but it was recorded wrongly) through to their not actually being married. It may be that they had been married and were living elsewhere - possibly with older children - perhaps not even in Hertfordshire.
Ideally you need to know more about them but they lived in a period when records were less helpful than the mid 19th century and it is important to collect every bit of information you can as you never know where a vital clue will crop up. I would suggest you look for the family on the microfilmed 1841 and 1851 census returns for Hatfield - which you should be able to order for viewing at the nearest LDS Family History Centre in Sydney (address on familysearch) . If John and Sarah lived until the 1851 census you will get to know their ages (and hence date of birth) and also their place of birth. Failing that the less informative 1841 census could show members of the family living together. The burial register is probably also available on microfilm and will give the age at death - which gives a date of birth. There may also be a relevant tombstone inscription, and you might like to check the Hertfordshire Family and Population History Society web site to see if they have published a memorial index for the Hatfield parish church.
I checked the 1823 and 1839 Pigot's directories, and the 1850 Post Office Directory and the only Clark I found under Hatfield was in the 1839 directory where one of the entries under the Taverns and Public Houses heading is "Chequers, James Clarke, Hornbeam Hall."
It is possible that the John CLARKE, the son of John and Elizabeth Clarke, who was baptised at Hatfield on 20 April 1788 is Mahala's father - but that family chose more conventional names so I would not be in a hurry to accept this without more evidence.
You probably already know about them but I did a quick check on the 1881 census for the children. Ambrose Clarke was a 57 year old cab driver in Islington, London. I guess that Isabella was the 61 year old widow, Isabella Pates, a former domestic servant living at nearby Ayott St Peter with relatives. In addition there is a Mahala Jarvis, a 54 year old widow born at Woodside [Hatfield] who was a laundress living in London Road, Flamstead with a son and two daughters.