These letters detail the progress of the survey carried out by John Rennie from 1812 to 1815, which was funded by public subscription. It was not decided whether the link should be a canal or railway at this stage. The letters delineate the relationship between Rennie and the Committee, Raisbeck was frustrated with Rennie's lack of communication and slow progress, which was caused by Rennie's ill health. There also appears to be some miscommunication between the two parties over the need to survey for a railway in addition to a canal.

Some of the letters are addressed to George Raisbeck [or alternatively 'Riesbeck'], there seems to be some confusion on the part of Rennie over Raisbeck's forename as there wasn't a member of the Raisbeck family called George at that time, Rennie may have misread the contractiono of Raisbeck's first name, Leo., as Geo., the latter being the short form of George.