Shropshire Routes to Roots

During that period, the land we now know as Shropshire experienced varying climates from tropical to temperate, and the different type of weather associated with each. For long periods the land was under water, and it was during these periods that the different forms of sediment were laid down and compacted into the different rocks we see today.

Many of the shales were laid down in times of cool climate, while the sandstones of the North Shropshire plain were the result of harsh desert conditions, where winds ground down the exposed rock. As Shropshire rose and fell on its journey north, there were times when the weather was very warm and wet. Here the coal seams were laid down as the remains of ancient tropical forests, and in the warm seas, shell fish died and left their bodies as the limestones of Wenlock and Llanymynech.

Water in its various forms of rain, hail, snow and ice has a different effect according to its state. In its liquid form it erodes and conveys sediments to other locations. As it does so, it creates deeper and deeper valleys, removing the softer rock and leaving the harder beds as ridges. The steep Carding Mill Valley on the Long Mynd is typical.

In its solid form as ice, it has a very powerful splitting action on exposed rocks. Water expands as it freezes, so if it collects in a rock crevice, it pushes outwards, weakening, then splitting off splinters of rock.

The shape of much of Shropshire's upland landscape has been formed in this way, with fine examples of frost weathering on most mountain tops.

Sun can have a similar effect. In the heat, the exterior of the rock expands, while the centre remains cool and static. When the rock cools at night, the surface shrinks back. This constant to and fro eventually flakes off a piece of rock. This is known as "exfoliation".

Put together hot days and frosty nights and their combined action can very quickly break down even the toughest of rocks.

Wind is most spectacular during a storm, but wind of any kind has an effect on the landscape. It is its ability to carry fine particles of dust that is its secret. These particles act like a fine sandpaper on anything they meet, and exposed rocks are most vulnerable.

Where people walk, the top layer of grass or soil is removed. Soon the wind removes the remainder, leaving the rocks exposed to more rapid weathering than would have been the case had the footpaths not been created.