The J.W. Fenwick manuscript, compiled in the second half of the 19th century, is a compilation of Northumbrian pipe music, together with other material associated with the instrument. Fenwick was a tailor, who lived in North Shields from about 1841. The same town was the home of the Reid family of pipers and pipemakers, and several other prominent pipers lived nearby. By 1894 Fenwick was described as "one of the oldest and best-known small pipes players in the county"; by this time he seems to have been playing for about 50 years. The manuscript was apparently being compiled throughout this period.
This source is particularly important, in that for many of the tunes Fenwick is careful to indicate his source for the version he gives. For instance, in some cases Fenwick gives a provenance from Cornelius Stanton, and occasionally via Stanton to John Peacock. Two of the tunes from Stanton, in Stanton's own hand, Little wot ye wha's coming and Blackett of Wylam were attributed by him to Peacock, although it is not in the collection of Peacock's tunes published about 1800. These tunes are also known from the manuscripts of Peacock's pupil Robert Bewick, but any direct association of them with Peacock had previously been conjectural. Another important group of tunes have an attribution to Robert Reid, or his children James Reid and Elizabeth Oliver. One of the Reid tunes is a 5-strain set of The Dorrington Lads, from Mrs Oliver, whose comment is noted that "This is most likely the same copy that poor Will Allen was trying to play when his Spirit was called Home to a more blissful Rest". This version was known, from the Rook manuscript, but its association with the Reid family was not. Given Robert Reid's father Robert Reed's known association with James Allan, this link is entirely possible. Further, some tunes or versions are otherwise unknown - a version of Shew's the Way to Wallington, from James Reid, is distinct from previously known sets.
One long variation set, of six strains, on the tune "Highland Black Laddie", called "Highland Laddie" in the manuscript, is attributed to Robert Mackintosh, a Scottish violinist and composer, whose son Abraham had settled in Newcastle; it seems to be unknown elsewhere, but an unusual variant of the same tune in the Rook manuscript, also called "Highland Laddie", is thematically related to the final pair of these variations - together they suggest that the original composition had eight strains.