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22. The Geology of the Dorset Coast (2016) 2nd Edition


by John C. W. Cope

The Dorset coast has provided the training ground for many aspiring geologists and also attracts amateur geologists in large numbers. This guide provides information that will be accessible to those from all levels of geological background. In addition to the description of the succession, the guide covers many other aspects of the geology as they arise and includes information about access. The new second edition includes updated stratigraphical details and benefits from data and new interpretations by Malcolm Butler (chair of UK Online Geophysical Library) of six north-south seismic lines over the county. These enhance the value of the guide and add a further dimension to the geological descriptions. The seismic profiles can be downloaded at a larger scale from the UKOGL website (www.ukogl.org.uk).

The Dorset Coast displays a virtually unbroken succession of largely marine rocks varying in age from latest Triassic to Mid Eocene and this guide traverses the succession from Pinhay Bay in the West to Mudeford east of Poole Harbour.

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Itineraries
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The Dorset coast has provided the training ground for many aspiring geologists and also attracts amateur geologists in large numbers. This guide provides information that will be accessible to those from all levels of geological background. In addition to the description of the succession, the guide covers many other aspects of the geology as they arise and includes information about access. The new second edition includes updated stratigraphical details and benefits from data and new interpretations by Malcolm Butler (chair of UK Online Geophysical Library) of six north-south seismic lines over the county. These enhance the value of the guide and add a further dimension to the geological descriptions. The seismic profiles can be downloaded at a larger scale from the UKOGL website (www.ukogl.org.uk).

The Dorset Coast displays a virtually unbroken succession of largely marine rocks varying in age from latest Triassic to Mid Eocene and this guide traverses the succession from Pinhay Bay in the West to Mudeford east of Poole Harbour.

WEST DORSET
Pinhay Bay to Lyme Regis
A falling tide is necessary for this section of the coast, accessed by the coastal path from the Cobb.
Start point western end of car park on south side of the A3052 above the Cobb at Lyme Regis SY 338 916

Lyme Regis to Charmouth
Traverse during low tide and recommended to be undertaken from Charmouth, as a return to there may be made at most stages of the tide.
Start point small Pay and Display car park on Chramouth seafront SY 365 930

Charmouth to Seatown
Approach the coast from Charmouth via Lower Sea Lane. Due to the risk of cliff falls it is imperative to venture any distance beneath this cliff on a falling tide and preferably with up-to-date local knowledge.
Start point small Pay and Display car park on Charmouth seafront SY 365 930 Seatown to Eype Mouth
It is possible to follow this itinerary and the next (onwards to West Bay) in an afternoon. The cliffs along this stretch of coast are precipitous and it is most unwise to try to examine them at any point other than at beach level.
Start point car park at Seatown SY 421 918

Eype Mouth to West Bay
Accessed by a very narrow road off the A35. A major change in geology can be seen eastwards brought about by the Eype Mouth Fault.
Start point car park at Eype Mouth SY 448 911 (very restricted parking and often not open outside of the summer months)

Bridport
Bridport is the principle town in west Dorset which is situated primarily on the Dyrham Formation but the eastern part of the town is on the alluvium of the River Brit which for some distance follows the Mangerton Fault. There are several Pay and Display car parks in Bridport but the most central is Ropes Walk.
Start point Ropes Walk car park SY 465 928

West Bay to Burton Bradstock
This section is backed by two similar dramatically yellow cliffs; the western one is East Cliff and the eastern one Burton Cliff. Access can be gained in several ways via the footpaths above and below the cliffs.
Start point National Trust car park at Southover SY 492 887

SOUTH DORSET
Abbotsbury and Porlesham areas
This itinerary takes in a number of stops which are designed to be visited by car.
If visibility is good it is worth stopping at the View Point on the B3157 (SY 561 860) which gives views of the Isle of Purbeck and Chesil Beach, right across the Weymouth Anticline.
Start point View Point on the B3157 at SY 561 860, if visibility is good

Bathonian and basal Callovian of the Fleet coast
Most of this itinerary is on private land and permission must be obtained before attempting accessing (contact details supplied in Guide itself). None of this coast is suitable for large parties as parking for more than one or two cars is frequently difficult.
Start point East Fleet at SY 636 801

Callovian, Oxfordian and basal Kimmeridgian of the Fleet coast
Although waves of The Fleet continue to expose fresh material exposures here are poor with the sections of the Corallian Group to be regarded as supplementary to the fine sections to the north-east of Weymouth.
Start point Tidmoor Point (access is not permitted when red flags are flying) SY 643 786

Oxford Clay, Corallian Group and Kimmeridge Formation on the coast south of Weymouth
Again discontinuous exposures in the Corallian rocks to the south of Weymouth to be regarded as supplementary to the magnificent sections around Osmington Mills and Ringstead covered by this itinerary.
Start point pay car park at The Nothe SY 686 787

Isle of Portland
The island forms the most southernmost extremity of the southern limb of the Weymouth Anticline, and on it rocks from the upper part of the Kimmeridge Clay Formation to the lower part of the Purbeck Limestone Group crop out. Access to West Weare Cliffs requires some scrambling and is not recommended for larger parties.
Start point Victoria Square, Chiswell (SY 682 738)

The Weymouth Relief Road
Offers several exposures through the northern limb of the Weymouth Anticline.
Start point Upwey SY 671 845

Browleaze Cove to Ham Cliff
Access the beach from the road and walk westwards beneath Furzy (Jordan) Cliff.
Start point car park above Bowleaze Cove SY 720 820

Ringstead Bay and White Nothe
From the car park in Ringstead there is a fine view of the Holworth House unconformity, with the Chalk Group, Upper Greensand and Gault Formations dipping south, and the Kimmeridge Clay Formation, Portland Group and Purbeck Limestone Group dipping northward.
Start point Ringstead car park SY 751 815

The Abbotsbury and Ridgeway Faults northeast of Weymouth
The Abbotsbury and Ridgeway Fault systems are well exposed in the area to the north-east of Weymouth. Structures along this fault line can be examined in several discrete sections best accessed on foot with only limited parking available.
Start point B3159 adjacent to Gould’s Hill SY 660 859

PURBECK AND EAST DORSET
The Lulworth area
This is a classic area of study of structures displayed in the northern limb of the Perbeck Anticline, the stratigraphy of the uppermost Jurassic and the Cretaceous and costal erosional features. Access will be will be needed to the Lulworth Army Ranges and opening times can be found here.
Start point Pay and Display car park at Lulworth (SY 822 801) is expensive but free for educational parties in minibuses or coaches

Warbarrow Bay
When the Lulworth Army Ranges are open Worbarrow Bay can be visited providing good views of the Purbeck Anticline.
Start point deserted village of Tyneham SY 882 801

Kimmeridge Clay of the type area
Access to Kimmeridge is via a toll road belonging to the Smedmore Estate and all roads leading to the area are off limits to coaches without permission beforehand.
Start point car parking at Kimmeridge Bay SY 909 791 & SY 910 788

Portland Stone of Purbeck
The succession through the Portland Group is exposed in its entirety in eastern Purbeck.
Start point car park south of Renscombe Farm SY 964 774

Durlston Bay
Safety should be emphasised in studying this section as parts of the cliffs are quite unstable. Durlston Bay is the type location for the Purbeck Limestone Group and can be accessed from the centre of the bay or from the northern end at Perveril Point.
Start point Perveril Point car park SZ 035 785

Swanage Bay
The broad sweep of Swanage Bay from Perveril Point in the South to Ballard Point in the North is entirely over the outcrop of Cretaceous rocks.
Start point Perveril Point car park SZ 035 785

Studland Bay
Accessible at all but high tide. If travelling by car follow signs to South Beach and park at the southern end of the bay in the National Trust car park.
Start point Studland Bay National Trust car park SZ 038 825

Poole Harbour to Mudeford
This area consists of Palaeogene rocks with a very gentle easterly dip. Steep-sided valleys, called chines, cut through these rocks and provide access to this stretch of highly developed coast line.
Start point car park at Poole Head SZ 050 885

Map of Itineraries