The valley of the Derwent provides an important communications route. Between Derby and Rowsley the valley is followed by the A6 road , which was the main road from London to Manchester until the creation of the motorway network, and is still a busy single-carriageway road. The former Midland Railway 's lines from Derby to Sheffield and Manchester also followed the Derwent, the former as far as Ambergate and the latter as far as Rowsley. The Sheffield line still operates as part of the Midland Main Line , but the Manchester line was severed north of Matlock in 1968, and the section from Ambergate to Matlock now forms the Derwent Valley Line , a single-track branch line. Between Ambergate and Cromford, the river, road and railway are also paralleled by the Cromford Canal .The terminus was once connected to Manchester across the High Peak by the early Cromford and High Peak Railway .