[5][6][7] In 1863 a group of mill owners from Manchester, led by William McConnel, leased the quarry.

Cotton shortages, caused by the American Civil War, had reduced the production of the mills and they were looking for other profitable enterprises.

They formed the Aberdovey Slate Company Limited, to operate and manage the quarry, and planned to increase production at Bryn Eglwys.

The main barriers to the quarry's expansion at the time were the transportation arrangements for finished slates, and the lack of a workforce near Bryn Eglwys.

[2] Neither the quarry nor its associated railway were great commercial successes, and by 1879 the company had run out of funds.

[10] In 1911 the local Liberal Member of Parliament, Henry Haydn Jones, purchased the quarry for equivalent to £707,486 in 2023, along with the Talyllyn Railway and the village of Abergynolwyn.

[12] Despite the closure of the quarry, Haydn Jones kept a passenger service operating on the railway until his death in 1950.

Bryn Eglwys was sold to the Forestry Commission, and the surviving quarry buildings were demolished in the early 1980s.

Three parallel veins of Ordovician[15] slate run through mid Wales, from the region north of Dinas Mawddwy through Corris and south west towards Tywyn.

These veins are the southern edge of the Harlech Dome anticline which surfaces in the north at Blaenau Ffestiniog.

[15] Where the veins pass through the site of Bryn Eglwys, they are inclined at an angle of about 30 degrees from the horizontal, sloping downwards to the south-west.