Geology

Devon is unique among UK counties in lending it’s name (since 1840) to a geological period of time 416–359 million years ago. During the Devonian Period fish proliferated and evolution of the jaw took place. Who knew Devon was a geologists’ paradise with 13 main rock types, and can boast a history of being tropical, almost desert-like, submerged, and weathered by permafrost over the millenia! 

Geologists are also very familiar with Sticklepath, as it gives its name to the Sticklepath Fault which includes Belstone Cleave, the valley shown on the topographical map I shared previously. 

Also known as the ‘Sticklepath – Lustleigh fault zone’ and similar variations, it runs NW to SE from Bideford to Torbay, through Sticklepath and Lustleigh.  

This accounts for the historical mines and quarries in the area, utilising veins of copper, the presence of arsenic and tin, as well as granite for building and stone for road building.  The Sticklepath Fault seems best known for the ‘ball clay’ sediments found at a few places along its length, used for pottery since the 17th century and exported since mid-19th century.  

“it is highly plastic and can be formed into intricate shapes like tea services and toilet pans that can be handled before firing in a kiln without undue risk of damage. Moreover, after firing it has a light colour, unusual in most other clays.” (geo-devonrocksgeologyguide.pdf)

The main mineral is kaolinite, as in China Clay but with a different crystalline structure. The fact it is largely free of iron oxides gives it the light colour (unlike many clays which are reddish and used for brick-making).  The Sticklepath Fault provided an almost unique set of circumstances which allowed formation and maintenance of these ball clay pits: erosion of rocks into fresh or brackish water; trapping the ultra-fine particles before they could be washed out to sea; with little subsequent erosion or deeper burial of the sedimentary deposits. 

A good map showing the Fault and distribution of the rock types can be seen in:

Devon’s rocks – a geological guide

An interesting detailed report with lots of photos can be seen:

geo-devonrocksgeologyguide.pdf