The geology of Merseyside in northwest England largely consists of a faulted sequence of Carboniferous Coal Measures rocks overlain in the west by younger Triassic and Permian age sandstones and mudstones.
Quarries opened up in the Chester Pebble Beds and Helsby Sandstone formations have provided building stones as used in Liverpool Anglican Cathedral and Lime Street station for example.
The most significant is the north–south oriented Boundary Fault which runs west of Widnes, St Helens and Skelmersdale and marks the western edge of the Carboniferous Coal Measures outcrop.
The Triassic rocks of Wirral are affected by the Caldy, Grange, Thurstaston, Frankby, Greasby, Woodchurch, Seacombe, Barnston and Neston faults.
Elsewhere in the St Helens area, the coalfield is broken by the generally NNW-SSE aligned Roaring Meg, Derbyshire Hill and Twenty Acre faults.
[5] Subsequently, coastal and estuarine sands, silts and muds have been deposited widely throughout the Mersey and Dee estuaries whilst alluvium fills the floor of other river and stream valleys.