All these years later, I can add to this story, thanks to online newspaper archives.
South Wales Daily News 22nd August 1885
Penwyllt Mountain Railway
This railway, commenced about six weeks ago, is rapidly approaching completion under the management of Mr. Wm. Jones, contractor, of Neath. The total length is three miles, and only a few hundred yards of earthwork remain to be moved before the metals are laid down. The line is the private property of Messrs Kershaw and Pole Limited, 27, Leadenhall-street, E.C., well known in the South Wales district for their silica bricks. The railway will be worked by them in conjunction with the Midland Company, and will open up a new district for limestone, lime, and silica sand, invaluable for steel works. The construction is the most remarkable in the country for an ordinary 4 feet 8 1/2 inch railway, unlike any existing line, and has been visited by several engineers of note. The plan and sections have been jointly made by Mr. Jones, the contractor, and Mr. D.M. Davies, engineer, of Neath. A lot of needless opposition was raised by a commoner in Brecon against the promoters, which caused them to incur a great deal of unnecessary expense and trouble. Fortunately, the difficulties have all been overcome, and a large trade may be expected from Penwyllt through the opening of this branch.