Tag Archives: Unconformity

The Ercall

Due to some technical issues with my computer I haven’t posted anything in a few weeks.  Now I’m back up and running I plan on posting on a more regular basis.

Today’s monologue is about a fantastic geological site next to the Wrekin; the Ercall.

Location: The Ercall (pronounced ar-cal) is just north of the Wrekin in Shropshire, at around 52*40′ North, 2*31′ West, less than 1 km south-east of Junction 7 of the M54.

Access: The Ercall is open to the public at all times and access is easy.  There is a well maintained path and for the main quarry the gradient is low.  Other areas of the hill can be a little steep so if you have any mobility issues then they may be a little difficult to reach.  You can walk or scrabble over pretty much the whole hill as there are multiple small paths coming off the main track.  There are several small quarry holes as well as the main quarry and the whole place is worth exploring.

Geology: The various quarries in the Ercall are a fantastic place to see several geological features.  WARNING: wear a hard hat if you going to get close to the cliffs as there is the risk of falling rocks.

The featured image above is in the main quarry and shows a feature called an unconformity; specifically a nonconformity.  This is were there is a break in the rock sequence.  A nonconformity is the boundary between an underlying layer of igneous or metamorphic rock and an above layer of sedimentary rock.  In this case the igneous rock to the left of the image is an orange-pink coloured granophyre.  This is related to the Uriconian volcanics and is about 560 million years old.  The rock to the right of the picture is a pale grey Wrekin Quartzite and is about 533 million years old.  It is one of only a few places in Shropshire that you can see Cambrian aged rocks.  The Wrekin Quartzite is a bit missed named as a true quartzite is a metamorphic rock not a sedimentary one as found into the Ercall.

DSCF4928

The above image is a close up of the nonconformity.  Mixed in amongst the quartzite are several layers of conglomerate (see below).

DSCF4925To the east of the the nonconformity the quartzite mixes with the Lower Comley Sandstone and you get some impressive examples of a sedimentary bedding planes.  These are well jointed and are an excellent example.  These bedding planes have been lifted and incline downwards to the south-south east.

DSCF4916There is one more geological gem (figuratively speaking) to be found at the Ercall; ripples.  Mixed in in the layers of conglomerate are some wonderful examples of ripples.  These can be found higher up at both the west and east sides of the main quarry.  The ones to the west are in slightly better condition.  They can best be seen on a slightly cloudy day, just after it’s rained as the light & shadows more clearly define the ripples.

DSCF3340DSCF3354Combining this with the conglomerate, sandstone and quartzite gives us the origin of these rocks; an ancient beach.

For such a small site the Ercall really does have a wide range of geological features that can be seen really easily.  They’re great examples of nonconformities, bedding planes and ancient beaches.

Other Stuff: The Ercall is a nature reserve operated by the Shropshire Wildlife Trust, and a wide range of wildlife can be seen. There is a mixed deciduous forest with a small  stream running through it.

DSCF4881In spring the forest floor is covered in bluebells.

The local animal life is typical of a British woodland.  You can see finches, woodpeckers, Nuthatches, Treecreepers, Common Buzzards and if you’re really lucky a Peregrine Falcon.  It is a great place for a casual walk and has some wonderful geological sites to see.

Reference: Geology of Shropshire (2nd Edition) by Peter Toghill (2006), Geology (2nd Edition) by Stanley Chernicoff (1999).