Up to twenty wagons laden with slate were hauled by sets of horses between the inclines and this system worked efficiently for 75 years until it became apparent that such was the demand for slate, certain improvements would have to be carried out.
The first such modification came in the form of the Tyn-y-Clwt Incline deviation, this meant that the incline nearest the quarry and the level crossing on St Anns Road could be avoided in the form of a 1 in 34 deviation and the construction of a bridge over the road. This new mile-long section was designed and constructed by the Penrhyn Estate in 1876 and is now part of land available to rebuild the railway.
The next major development was designed by Spooner of Ffestiniog fame and incorporated a major deviation at the head of Dinas incline with the new route deviating sharply West into the village of Tregarth and gradually veering almost due North. This new section was very picturesque, running mostly through woods alongside the Afon Cegin before entering Port Penrhyn. The length of the whole line was then about six miles. Spooner also came up with suggestions for locomotives and enclosed coaches - all of which were rejected by the Penrhyn Estate.
Early motive power consisted of a trio of unique horizontal boilered DeWinton locomotives supplied in 1876, Edward Sholto (the first), Hilda and Violet. These locomotives although not by any means successful, worked the new railway until the arrival of the first Hunslet, Charles, in 1882, followed by Blanche and Linda in 1893. A wide variety of steam locomotives followed, including the famous “quarry” Hunslets and a number second hand from a variety of sources.
After 167 years of service the Penrhyn Quarry Railway was closed in June 1962, most of the locomotives finding new homes throughout the world.