The Ice Age in Lancashire – Forming the Landscape
At the height of the last Ice Age (300,000 to 700,000 years ago), the whole of east Lancashire was under a gargantuan sheet of ice. Near Whalley and atop the Yellow Hills, scratch marks can be seen on rocks.
These were formed by shards of stone, trapped in the ice, moving over the surface of the landscape.
Two glaciers met on the edge of Blackburn. One was coming south west from the Pennines, whilst the other had turned east around Preston, having originated in the Lake District to the north.
Sand and clay were left behind when the glacier melted, along with pebbles and boulders, deposited after being either carried atop or pushed by the glacier.
These deposits provided obstacles to the movement and escape of meltwater in some areas, leading to the formation of huge lakes.
A sandbank was left at Pleasington, going into Livesey, later being quarried (the pits from which the sand was extracted are still clearly visible in the area). Stretching back to the east of this for twelve miles was Lake Accrington.
Drainage channels from the lake were formed in two ways: either by the bursting of a natural dam (as is seen east of Darwen) or by the formation of a new course through the rock, such as the steep-sided valley of Hoghton Gorge.
After this drainage continued awhile, the level of the lake began to decrease, forming two new lakes – a reduced Lake Accrington and, to its west, Lake Blackburn. The main drainage channel for the former was the Irwell Valley, whereas Lake Blackburn drained largely through Cadshaw Valley.
To the north of Lake Blackburn, a subsidiary flow above the watershed cut a channel through the gravel and clay at Intack, where the flow, the infant River Blakewater (a. k. a. Knuzden Brook) flowed through a valley fifty feet in depth to Whitebirk. From there, the river followed the floor of the valley to Little Harwood and on to Blackburn and witton.
