Parking is available at N56 25.534 W003
32.074. (The gates can sometimes be closed, so
it’s best to park here and avoid getting shut in!). Walk down
the road past the houses and then bear left towards the start of
the path at N56 25.505 W003 32.184. From
here it’s just a very short stroll down to the river bank.
This path can be muddy and slippery and please note that the River
Almond is a spate river and its flow can change dramatically
overnight after a heavy rainfall.
The River Almond slices its way through various areas of
sandstones and mudstones along its route near here, more
dramatically on the outside of bends, as you can see at this quite
impressive spot. The river still continues its persistent erosion
of this area, which is apparent by the large amount of sandstone
lying on the river bed and on the banks.
The sandstone you are looking at originates from the Devonian
Era, a period from about 415 to 355 million years ago. The red
sandstones and mudstones were laid down at a time when the UK was
situated near the equator and when the continental plates of East
Avalonia, Laurentia and Baltica all collided to form a new
continent (the Old Red continent), resulting in a mountain range
that extended from what is now Scandinavia, through Scotland to the
Catskill Mountains in America.
An Almighty Collision...
Erosion of the mountain belt produced the sediments of the Old
Red Sandstone. In the arid climate, these sediments were deposited
during flash floods by braided river systems draining the
Highlands, which were then very high mountains, across the Midland
Valley of Scotland.
Braided rivers are those which, due to the very high
concentration of sediments contained within them, form a network of
small channels separated by small and often temporary islands
called braid bars. They deposit a huge amount of sediment.
Sandstone is a sedimentary rock, most types of which are made up
of quartz and/or feldspar, the two most common minerals in the
Earth’s crust. There are two stages in its formation.
Firstly, the layers of sand deposited through sedimentation by a
river, lake or sea (or even the air) accumulate and secondly, they
become compressed by subsequent deposited layers and cemented
together by the precipitation of minerals within the pore spaces
between the sand grains.
In this case, vast barren floodplains traversed by braided
sediment-choked streams would have presented a harsh and oxidising
environment for minerals, and would have resulted in the release of
iron oxides in large quantities.
The presence of iron oxide (haematite), a typical deposit
indicating that the source material is of arid origin, can lend the
sandstone a pinkish hue, right through to a dark red.
Sandstone can be any colour though, but the most common are tan,
brown, yellow, red, grey and white, depending on their
mineralogical makeup. For example, the presence of manganese can
give sandstone a hint of purple.
As should be apparent from looking at the cliffs, the sandstone
bedding has been tilted by tectonic movement, which creates
repeated small falls in the river. These falls, taken cumulatively,
can result in drops of several meters and to take advantage of this
natural energy, weirs were built with diverting gates, redirecting
some of the river flow into small canals called lades. The water
flow in these lades was then used to power water wheels for various
industrial and domestic uses. (If you continue on to Snaik’s
cache GCRMJ1 – Cromwellpark, you will see an excellent
example of a lade along the way).
At a couple of locations nearby, the River Almond’s path
is vertically sliced by igneous dykes, which are formed as the
result of magma intruding through lines of weaknesses in the crust.
Dykes cut vertically through strata, as opposed to sills, which
exploit horizontal weaknesses.
The Formation of Dykes and Sills
There was volcanic activity nearby during the same period, to
the south of Perth (the Ochil Hills) and the effects of this
activity are visible here. These rocky intrusions are harder than
the sandstone, and cause the river to narrow, creating conveniently
solid places on which to build weirs or bridges, such as the bridge
downstream at Almondbank or the one at Dalcrue further west.
To log this Earthcache, please visit this location and then
email me with the answers to the following questions:
1. Estimate the height of these cliffs from the
river to the base of the trees on top.
2. The presence of which substance could explain the
distinctive colour of the sandstone here and what sort of climate
it is typically representative of?
3. Name a common mineral component of
sandstone.
4. Looking at the face of the cliffs it is apparent
that the sandstone bedding is tilted, but in which direction does
it slope downwards? From right to left or left to right? (As you
look at it)
Please don’t post any of these answers (or photographs) in
your log, as actually visiting this location is the main
surprise.
Thanks for visiting and I hope you enjoy it!
