 This situation continued until 1893, when they were finally able to buy the remaining two shares from Holt's descendants.Thus, although trade on the river had only lasted for a little over forty years, the company lasted on paper for 173 years.Both the original bill presented to Parliament in 1713 nnd the second attempt in 1720 were supported by noting the coal pits, and the delfs, a local word for a mine or quarry, of stone and slate, the transport of which would be much easier if the river was navigable.