Press letter books, 1878-1920, press invoice books, 1878-1919, account books, 1893-1920, and a minute book, 1900-1901.

A copy of 'The Croesor file', comprising Adrian Barrell's and others' research material relating to the Croesor Slate Quarry, Llanfrothen, Merionethshire, from the 1860s onwards (1994 donation). A supplement copy to 'The Croesor file', also including extensive extracts from the Minute Book of the Park & Croesor Slate Co., and a section dealing with the research note books of Moses Kellow, the company's manager and engineer, together with a CD which contains the full autobiography of Moses Kellow (2003 donation).