Geology of Gloucestershire

These varying rock-types are responsible for the three major areas of the county, each with its own distinctive scenery and land-use - the Forest of Dean in the west, bordering Wales, the Cotswolds in the east, and in between, the Severn Vale.

The Forest of Dean, situated between the rivers Severn and Wye, is formed of a raised basin of Palaeozoic rocks folded in the Variscan Orogeny, similar to the South Wales Coalfield to the west.

Impressive cliffs have been cut by the river in lower dolomitic sections of the Carboniferous Limestone, most notably at the popular ‘Symonds Yat’ viewpoint, which affords one of the most famous views in England.

This is superbly illustrated at the ‘Garden Cliff’, Westbury-on-Severn (see picture), where the river Severn has sliced a convenient ‘cut-away’ section of this transition from the red Triassic marls, through the thin Penarth Group (formerly 'Rhaetic') strata, to the lias clays and limestones of the lower Jurassic.

A sheet of mainly Jurassic limestone fan gravel probably covered most of the vale in the past but has since been eroded away leaving isolated deposits, most notably the Cheltenham Sand, which forms a well-draining light soil in the Cheltenham-Gloucester region.

The Middle-Jurassic oolitic limestone series which forms the bulk of the Cotswolds hills contains the best-known of the county's rocks on account of its extensive use throughout the area as a building stone.

All from churches to humble cottages have been imbued with a mellow, warm character from the golden yellow colour of the stone - to which many ‘honey-pot’ Cotswold towns owe their modern popularity and prosperity.