September – Whinstone

admin — Thu, 10 Sep 2009 17:53:12 +0000

Whinstone is a quarryman’s term for a variety of hard, dark-coloured, rocks including basalt and chert. Here, in the Tees Valley and Cleveland, the name refers to a hard rock that is very different from the soft sedimentary strata which make up the majority of the area’s underlying geology.

Around 58 million years ago, as the Atlantic oceanic basin formed, adjacent areas of crust became stretched and weaknesses could be exploited by molten material (magma) being forced into the crust by pressure from below. This magma cooled very quickly surrounded by local rocks and became the Cleveland Dyke.

Stretching for c.350 miles between Mull in Western Scotland and the Tees Valley and North Yorkshire the hot magma cooled to form a dark blue-grey, finely crystalline rock referred to by geologists, more correctly, as dolerite. Dolerite is chemically similar to basalt, the major difference being that basalt is erupted at the Earth’s surface, whereas dolerite solidifies within the Earth’s crust.

Following removal of the overlying strata by erosion, primarily through glaciation, the dyke was exposed at the Earth’s surface. In the west of our region it can be traced crossing the river at Preston-on-Tees, but perhaps its most notable feature occurs near Great Ayton where the more durable rock making up the dyke, and softer Jurassic strata into which it is intruded, exhibit a phenomenon known as differential erosion. The softer sedimentary rock is preferentially removed by erosion leaving the harder whinstone to form a bold ridge called Langbaurgh Ridge.

The geater hardness of whinstone relative to sedimentary rock makes it ideal for use road-stone and cobbles, and it was for this purpose that Leeds City Council leased land around Great Ayton, where the ridge is best developed, in 1869. Large quantities of the rock were quarried at Cliff Rigg, as well as elsewhere along the length of the dyke, for example at Preston-on-Tees, Ingleby Barwick, and at a variety of locations on the North York Moors. The now-abandoned workings today form an unmistakeable scar on the landscape, though the former quarry’s remains allow geologists to study the effects of metamorphism, i.e. the baking of the surrounding sedimentary rock when the hot magma was injected.

Stainsby Beck Dyke

admin — Thu, 10 Apr 2003 15:35:29 +0000

Contents

Site Description
Site Map
Site Assessment
Surveyors

Grid Reference NZ 465 146
BGS Sheet 33
OS Sheet 93
Forwarded as RIGS 30/09/2003

Site Description

Site Status SNCI
Description of Geodiversity Stream bed exposure of the Cleveland Dyke
Literature References

Site Map

Site Assessment

Access and Safety	Comments	Rating
Safety of access	On footpath from industrial estate	10
Safety of exposure	On opposite riverbank footpath	10
Restricting conditions	High flow episodes obscure exposure	6
Multiple exposure	Mercia mudstone exposure downstream	7
Note	It is strongly suggested that on-site safety be the responsibility of the party leader(s), as the safety information above is given only as a guide.

Education and Science	Comments	Rating
Surface processes	Various fluvial processes	10
Geomorphology	Various fluvial features	10
Sedimentary rock	None
Igneous rock	Dyke intrusion	10
Metamorphic rock	None apparent
Fossils	None
Minerals	None specific
Structural features	Apparent dip of 2° & NNW orientation	7
Stratigraphy	Tertiary igneous intrusion	5

Geodiversity Value	Comments	Rating
Education	Various fluvial processes	10
Scientific	Small Cleveland Dyke exposure	5
Historical	None
Aesthetic	River corridor environment	10

Surveyors