The marriage was short-lived, producing as its only child the mathematician Ada Lovelace, but it was long enough to have been a drain on the Milbanke estate. The area’s fortunes changed when the Milbankes sold out to 3rd Marquess of Londonderry, who built a harbour, in 1828, to facilitate transport of goods from locally encouraged industries (the first coal mine was begun in 1845). However, this harbour later proved inadequate to deal with the millions of tonnes of coal and the 6th Marquess commissioned engineers Patrick Meik and Charles Meik to reclaim land and extend and deepen the dock. It was officially opened in 1905. The harbour is of particular interest because it consists of a series of interconnecting locks, rather than the more typical two wall construction.