This is a new webpage in the course of development.

Location

The quarry is situated west of Swanage in the Isle of Purbeck and north of St. Aldhelm's Head. It is NNE of the village of Worth Matravers. The map reference is SY 969783 and it is marked as Swanworth Quarries on the Ordnance Survey 1:25,000 Purbeck and South Dorset map. The quarry entrance is passed on the road from Kingston to Worth Matravers. There is no access at all to the quarry without permission from the owners, and it is not frequently visited by geologists. A public footpath (part of the Purbeck Way) passes up Hill Bottom and Coombe Bottom to the west of the quarry. In a few years time the quarry will cease working and the area will be landscaped to some extent. It is hoped that some good exposures will still be maintained for geological reference. Exposures of Purbeck marls are easily degraded and vegetated and so it is not clear how long sections of these strata will survive. This record here may thus be of some value in the long term.

Safety and Risk Assessment

General information regarding safety on Dorset geological field trips is provided in a separate webpage and you are requested to read this. This website simply gives descriptions of exposures and is not advice to visit or to collect at any specific place. No liability is accepted.

Swanworth or Worth Quarry is at the time of writing a working quarry and not a place of easy access. Although the geological features within it are well-worth reporting, it is not on most Dorset field-work intineraries and there is no access without permission from the owners. If it is visited the safety regulations of the quarry company must be followed strictly and these include safety helmets and high-visibility clothing. There are the usual quarry hazards at Swanworth with regard to cliffs, rocks, boulders, large dumper trucks, quarry machinery and blasting. The rock faces in working quarries are usually more hazardous than those of natural cliffs because the rock has often been loosened and the more unstable pieces have not slipped to the ground over the years. Safety helmets are essential. It is important not to hammer the chert in the Portland strata because dangerous splinters can easily penetrate the body and may cause blindness. When preoccupied in geological study take care not to walk backwards over a quarry cliff or fall down fissures in the Portland Stone. A hazard of injury exists if persons attempt to move or lift a large block of stone.

Introduction

This large quarry is worked for crushed stone or aggregate. It uses almost all the Portland Stone succession, including both the Portland Cherty Series, not usable for worked blocks of stone, and the Portland Freestone above, which is quarried elsewhere for building stone. The Portland Cherty Series and Freestone Series are well-seen in the coastal sections as at Seacombe, Winspit and St. Aldhelm's Head, not far away, and the sequence is not greatly different in this quarry. The Purbeck succession of thin-bedded limestone, shale and marl is of particular interest because it is not well-exposed at the coast near here, and the best coastal sections in the region are at Durlston BayDurlston Bay and Worbarrow Bay. The Purbeck succession is Lower Purbeck, including Caps, Broken Beds, "Cypris" Freestone, Hard Cockle and Soft Cockle Members. Strata above this has been eroded away.

Portland Cherty Series

Portland Freestone

The Portland Freestone is less porous and not such a well-developed oolite as on the Isle of Portland. It is similar to the Portland Stone in the coast sections of the Isle of Purbeck. It contains very little chert. Major joints with dissolution features occur at intervals. They are brown stained with travertine and with clay debris probably derived from the Purbeck Formation above during periglacial conditions. At least partly as a result of blasting the face of Portland Freestone is very fractured and does not contain the large unfractured blocks that are characteristic of the Portland Stones quarries of the Isle of Portland. This, of course, does not matter because the stone is all being used here in crushed condition.

Purbeck Formation

As noted above, the Purbeck succession seen here is entirely Lower Purbeck, including Caps, Broken Beds, "Cypris" Freestone, Hard Cockle and Soft Cockle Members. These units are visible towards the top of the quarry and strata above them have been eroded away.

These photographs above show the occurrence of the isopod Archaeoniscus brodiei in marls of the Lower Purbeck above the level of the "Cypris" Freestone Member. This lagoonal isopod occurs in various parts of the Purbeck Formation and seemed to have been able to tolerate slightly hypersaline conditions that occurred in the earlier part of Purbeck times (very early Cretaceous). It was related to the modern sea slater, also shown. It sometimes occur with fossil insect remains. The specimens in Swanworth or Worth Quarry are particularly well-preserved. Also shown are fish remains found in a loose block of Purbeck limestone nearby.