McConnel set about improving Bryn Eglwys to increase its output. He focused on providing rail transport for the isolated quarry, and in April 1864 he reached agreement with local landowners to purchase the land necessary to build a railway towards Tywyn and onwards to the port of Aberdyfi. Construction was well underway by July 1864. The standard gauge Aberystwith and Welsh Coast Railway was expanding rapidly from its base at Machynlleth, however, and in 1863 had reached Tywyn, so McConnel decided to build his line from the quarry to Tywyn, as the nearest point where slate could be transferred to the standard gauge railway. This was despite the line's initial isolation from the rest of the system because of difficulties in bridging the estuary of the Afon Dyfi to the south. An Act of Parliament (28 and 29 Vict, cap cccxv) allowing the company to operate passenger trains as a public railway was given Royal Assent on 5 July 1865, and the company appointed James Swinton Spooner as engineer for the construction. He laid out plans for a relatively straight line climbing steadily from Tywyn to the quarry and work quickly got underway. By September 1866 construction had advanced to the point where the Board of Trade inspector Captain Henry Tyler could make an initial inspection and report.