The Rhymney Railway (RR) had been incorporated in 1854 to link the Rhymney Ironworks with Cardiff. In 1858 the RR at last obtained running powers into Cardiff with a station near the TVR one on old Spital land, and with access to the eastern side of the Bute East Dock.
The further expansion of the coal industry, and in particular that of steam coal from the Rhondda Valley, led to John McConnochie producing a plan for a £2m new dock scheme, which the Bute Trustees put forward to Parliament in 1864. The scheme was rejected, however, on the grounds that the financial commitment was too great at a time when the Marquis of Bute was still a minor. In 1868, though, the Marquis came of age and Parliament then approved a smaller scheme to convert a small tidal harbour which had been provided some time before for the use of smaller vessels, freeing up space in the Eat Dock itself for the large vessels. The harbour was to be replaced by the large Roath Basin, which was opened in 1874, but even this was insufficient to cope with the demands of the coal exporters and the iron ore importers, and in 1882 powers were sought to build a further dock. Work commenced later in that year and in 1887 the Roath Dock was opened. The new dock was capable of dealing with the much larger ships which were now being used for both imports and exports.
The Marquis of Bute's financial interests in the docks were so great that from 1 January 1888 the ownership of the Bute Docks was transferred to a new public company, the Bute Docks Co., with William Thomas Lewis, engineer to the Bute Estate, as General Manager.