Hi Ruth
David Clarke married Married Mary Jane Harron 1888 Drumhome Parish Church (COI) Ballintra, David's father was Alexander Clarke, Mary's father was James Harron
Birth record from same church 1858 David Clarke, father Alexander Clarke, mother Margaret,
There were 2 Alexander Clarkes in the 1858 Griffth Valuation for the Parish of Drumhome
There was a Mary Harrow baptised in the same church in 1864, father James, mother Catherin, no suitable Harrons from time period, Harrow may be a mistranscription.
Regards
Joe