Complex sentence: On 19 February 1846 the line was extended all the way into the Duke of Buccleuch's recently built harbour at Granton, and became the Edinburgh, Leith and Granton Railway.
Split into simpler sentences: On 19 February 1846 the line was extended all the way into the Duke of Buccleuch's recently built harbour at Granton. At this point it became the Edinburgh, Leith and Granton Railway.