Richard Pennant, in 1784, obtained a Crown lease on the Hundred of Uchaf which included the parish of Llanllechid. In the same period he obtained the lease on Penybryn and built Port Penrhyn. This put independant slate producers at some disadvantage, which was further compounded when Dawkins Pennant in 1821 obtained the lease on the Hirael area and foreshore. Produce thus had to be carted to Bangor quay which I assume to be the area around and to the north of Dickies Boat Yard. Considerable assertions and dissent over the Uchaf lease lead to a Parliamentary Enquiry in 1822. Atkinson, Walker, Farey and others reported. Farey's report was unfavourable to the Pennant family. W. Hazeldine reported to Pennant that Bryn Hafod-y-wern was being well worked by J. Greenfield and 25 men but it seemed unlikely to find the valuable Penrhyn slate veins and that the quarries should be abandoned. In 1823, J. Trimmer from Middlesex, applied to the Crown for the lease of the Llanlechid quarries, which were awarded in 1824, when at the same time, Stanton reported that the valuable slate was unlikely to be found and that Penrhyn had fulfilled the terms of his lease. In 1825 John Evans ( Cilgwyn etc) had a tack note on the quarry. The Royal Bangor Slate Company Ltd. was established in London in 1845 and took over the working.Several attempts and much discussion between 1846 and 1854 failed to connect (at Abergwyngregyn) the quarry with the Chester-Holyhead railway. In 1852 the company became the Bangor Royal Slate Company. In 1873 100 men were employed. In 1882, 65 men produced 2198 tons of produce, in 1883 54 men produced 1263 tons.
Closure is variously reported in 1884 and 1885 but certainly the water supply was cut off on Monday, May, 27.1889.
Industrial unrest is documented in 1879, '81, '83 and '86 which might account for the assorted closure dates.
The quarry was surrounded by Penrhyn land and this peculiar situation was long a bone of contention both for the abstraction of water as well as deposition of waste water. The leat could well date from the time of Richard Pennant and is quite a bit of work. It starts at the headwaters of the Caseg, picks up the Afon Wen, follows the contours below Drosgyl and Gyrn Wigau and joins the headwaters of Afon Ffrydlas and runs around the S.W. side of Gyrn to the two reservoirs to the E. of the quarry.