The group comprises the following formations (in stratigraphic order, i.e., the oldest at the base and the youngest at the top): Each of these divisions has been given different names by different authors in the past including those shown in brackets above.

The sequence east of Lynmouth used to be referred to as the "Foreland Grits", and was thought to be somewhat older, and hence lower in the sequence, than the Hangman Grits[11] In March 2024 scientists reported the discovery of a fossilised forest of Calamophyton trees at a site near Minehead, its age being four million years greater than a fossil forest in New York State which had previously held the record as the world's oldest.

The overlying Lester Slates-and-Sandstones run from Widmouth Head, beneath the village of Combe Martin and on in a SSE direction to near Parracombe.

The Combe Martin Slates in turn extend from Beacon Point at Hele in a narrowing outcrop to Pinkworthy Pond and beyond.

Over the centuries the Brendon Hills have been mined for minerals, notably ironstone from which iron is extracted for making steel.

During the 19th century this activity reached a peak with the West Somerset Mineral Railway, including an 800 feet (244 m) incline, being built to take the ore to Watchet from where it was sent to Ebbw Vale for smelting.

[21] A geomorphological survey at Anstey's Coombe showed that mining had taken place at the site during both the Romano-British period and the 16th to 17th century.

[22] The Upcott Slates provide the coastal cliffs on the south side of Morte Bay and their narrow faulted outcrop continues east-southeastwards beneath Georgeham and to Winsham and Marwood.

The formation consists of sandstones, siltstones and shales including some feldspar and mica rich units, variously of marine through brackish to freshwater origin.

The formation extends eastwards through Barnstaple to the Buckland area where due to a syncline/anticline pair, the surface outcrop divides.

A thinner band of these strata continues east coincident with the valley of the River Yeo and the former railway to Brushford.

The outcrop broadens once again forming the country around Clayhanger and Waterrow before reaching its furthest east at Kittisford and at Nunnington Park, south of Wiveliscombe.

Whilst most of it is Devonian, the uppermost part of the formation is Carboniferous in age though the precise location of the boundary is difficult to determine.