DUP and Ulster Unionist councillors supported the suggestion to send the letters, as originally suggested by its Corporate Services Committee, but there was no recorded vote.
The decision to ask schools what plans they have to develop material in relation to "creation, intelligent design and other theories of origin" came at the end of an impassioned debate on the subject at Tuesday evening's monthly meeting.
It began when SDLP councillor and former school principal Peter O'Hagan said he did not feel the council should "be taking upon itself" to "interfere or get involved in the curriculum".
His comments were supported by his party colleagues councillors Matthew McDermott and Brian Heading. Mr Heading also warned such a move could herald the start of a 'witch hunt' against educators teaching evolution – something he claimed was already happening in the USA.
Sinn Fein councillor Paul Butler told the meeting he felt councillors should "stay out" of trying to tell schools what they should or should not include in their curriculum.
Corporate Services Committee chairman Ulster Unionist councillor Bill Gardiner Watson, also a former teacher, felt the same although he said the council was "entitled to express an opinion".
However, the DUP's Paul Givan, who made the original proposal, said he was not suggesting the council dictate what schools should or should not teach, but simply pointing out that under the revised curriculum there was an opportunity for alternative theories to be taught.
He said Sinn Fein Education Minister Caitriona Ruane had made the same point in the Assembly.
Mr Givan's comments were supported by his party colleague Alderman Edwin Poots, Minister for Arts and Culture, who made it plain he was a strong believer in biblical creation.
Deputy Mayor Ulster Unionist Ronnie Crawford appealed for cross-party support for Mr Givan's proposal, pointing out that Pope Benedict was a firm believer in creationism and adding there were many points on which he agreed with the Pontiff.
It was also suggested by several DUP councillors during the discussion that preventing the teaching of theories other than evolution was in itself a form of "fascism".