Flysch. Swiss Alps.

This specimen was a gift from Bill Fitches who collected it from the Salanfe valley in the Martigny area near the Swiss-France border in the Swiss alps. His description of the specimen is as follows. The Flysch is a suite of marine sedimentary rocks of Eocene age, which was deposited in the Tethyan ocean between the African and European continents just before they collided to create the Western Alp mountain chain. They are low energy  turbidites composed of thinly bedded mudstone and siltstone. The sample  has many veinlets of light coloured carbonate , probably calcite, which cut the bedding at right angles. They were produced during the plate collision and the rise of the Alps. The sample was squashed perpendicular to the bedding planes, and strongly extended along the bedding. This deformation caused lots of cracks which filled with carbonate segregating from the host rock to make the arrays of veins. The veins are in several directions, implying that the direction of extension changed during the deformation history.

Wrekin quartzite, Ercall quarry.

The Wrekin quartzite is exposed in Ercall quarry, Shropshire, from where this specimen was collected  The quartzite is composed of  fine pale grey quartz sand, consolidated by siiceous cement. It is lower Cambrian in age, and the quartzite is resting unconformably on the Uriconian volcanics.

Concretion. Trewern,Welshpool.

This concretion has a definite sharp edge around the broadest part, almost as though it is two halves stuck together. I am not absolutely sure, but I think it is of the type described as "cone in cone". The only way to be sure would be to break it open, which I am loathe to do. Concretions are fairly common in the Welshpool area, and I have heard stories that they were commonly used as doorstops. When it has been seen by young children they thought it was a dinosaur egg. It was collected many years ago at Dingle farm, Trewern, Nr. Welshpool in central Wales. There is a comprehensive explanation of concretions by Tony Thorp in issue No 1 of the Silurian magazine which can be accessed on this site.

Rhyolite. Ercall quarry, Shropshire.

Rhyolite is a silica rich extrusive igneous rock. These specimens were collected from Ercall quarry in Shropshire on a field trip in July 2001. They were picked out of the rubble at the foot of the quarry face, which was plentiful at the time. One of the specimens can be described as flow banded. Unusually, this picture was taken using a photocopier before digital camera was the norm.

Dolerite ( Diabase ) Criggion ,Welshpool.

This specimen of dolerite ( diabase ) was collected on a field trip to a local quarry in June 2001. The Criggion quarry, on the outskirts of Welshpool in Powys is well known for supplying very hard stone, mainly used for road surfacing.  The rock type is described as an albitised olivine diorite.  The mineralogy and appearance of the rock indicates a degree of chemical alteration due to reactions between original minerals and migrating fluids. The usual appearance of lath shaped plagioclase crystals is absent. Instead the dolerite has a spotted appearance. This assumption is due to my observation, and therefore a better description might be obtained by a laboratory investigation. Note the difference between weathered surface and exposed surface.