McConnel set about improving Bryn Eglwys to increase its output. In 1865 his company earmarked money for the construction of a narrow gauge railway connecting the quarry with the port of Aberdyfi. The standard gauge Aberystwyth and Welsh Coast Railway was expanding rapidly from its base at Machynlleth however. In 1863 this railway had reached Tywyn, so McConnel decided to build his line from the quarry to Tywyn. This was 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 186., 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.