According to Diane Baptie's Registers of the Secession Churches in Scotland the only surviving records from Wishaw (Wishawtown), Relief, UP, Thornlie UF, C of S are deaths 1835-46 and baptisms 1831-64. So the reason the marriages from this congregation have not been transcribed is that either they never existed, or they have been lost.
It is reasonable to suppose that they were Presbyterian, because most* Christian denominations except the Roman Catholic and Episcopal churches in Scotland were Presbyterian. That includes, specifically, the Church of Scotland, which is sometimes described as 'the Established Church'. 'Presbyterian' does not define the beliefs of a particular sect or denomination. It describes the hierarchy of that denomination.
The Roman Catholic and Episcopalian churches have hierarchies of bishops, but there are no bishops in Presbyterian churches. Each congregation has a Kirk Session, which is a committee made up of minister and elders. The next tier is the Presbytery, which is a committee made up of the ministers and (usually) one elder representing each Kirk Session. Then comes the Synod, which is a grouping of Presbyteries, and ultimately the General Assembly, which comprises the ministers and representative elders from all the congregations of that denomination.
*There were some Methodist, Baptist and Congregational congregations, but I am not au fait with the internal organisation of these denominations.