some coal measures and iron ore deposits, the final tunnel being lined through most of its length. By 1793 the company had a balance in hand of only £273 and the cost had risen to half as much again as Jessop's original estimate. Nevertheless, the canal was showing an income, unfinished though it was. In August, however, there were problems with the Derwent Aqueduct which required considerable modification. The spandrel walls had parted due to the horizontal forces imposed by the canal, and a longitudinal split had opened up in the arch. In his report to the canal committee, Jessop gave his opinion that the use of Crich lime, being unusually pure, had delayed the setting of the mortar. Later writers, with the benefit of engineering knowledge acquired after Jessop's time, have suggested that the spandrel walls were simply too slender for the forces imposed. At any rate, the arch was partly dismantled and steel tie bars and lateral reinforcing arches were installed, together with external buttresses. This Jessop did at his own expense. In the end, despite costing about twice the initial estimate of £42,697 (£ in ), the canal opened in 1794 and was a financial success. Operation Jessop had based his initial predictions for the expected returns on the carriage of limestone from Cromford and Crich and coal from Pinxton. However, the canal itself encouraged new enterprises. The canal mostly carried coal, lead and iron ore, some extracted from inside the Butterley Tunnel. Copper was brought from as far away as Ecton Hill in Staffordshire and the canal opening the way for lead from Ecton, as well as Wirksworth to be taken to the Lead Market at Hull and chert from Bakewell to the Potteries. It also allowed the finished products of the area to be exported widely, the Butterley Company's castings and Arkwright's spun cotton. The opening of the Derby Canal and the Nottingham Canal, both in 1796, further facilitated the latter's trade with these textile centres. Although Arkwright had suggested that water should be drawn from the Derwent (by raising his weir at Masson Mill and feeding it via an aqueduct to Cromford Meadows - thus improving his plans for quarries behind Willersley and adding extra power to his mill wheels at the expense of the Canal Company), the canal committee had secretly no intention of so doing. The Proprietors changed the line of the