The collection contains manuscripts relating to the various industrial activities of Searell in the following North Wales quarries and mines: Hafod y Llan, Sygun, Cwmorthin, Cwm Trwsgwl, Prince of Wales, Snowdon Slate, Deudraeth, Moelfre, Maenofferen, Braich yr Oen, Lliwedd Bach, Gallt-y-Llan, Croesor and Cefncam.
A large proportion of the collection comprises of correspondence with a Henry McKellar of London.
The collection also includes the Hafod y Llan Quarry bargain book, 1841; Sygun Copper Mine setting book, 1841-3; Cwmorthin Quarry accounts, 1844-5; regulations governing work at Hafod Quarry; a record of slates (from several quarries) shipped from Portmadoc, 1839-59; reports on the development of the Cwm Trwsgwl and Moelwyn Quarries, 1837-83; plan and sections of the Cwm Trwsgwl and Snowdon slate quarries and of the Deudraeth sett quarry; plans of railways through Sygun Bach and Sygun Fawr estates, from Hafod y Llan to Beddgelert and from Cwmorthin to Tanygrisiau; and five letter books covering the period 1857-67 relating to Searell's various industrial activities.