The waypoint is for an ancient scheduled monument. A bridge originally made entirely of limestone. Which has had to be repaired many times due to the erosion of the limestone.
Limestone used to be a good, cheap building material used extensively in many parts of the world.
All was (mostly) good until the industrial revolution and steam power became increasing popular in the 1700s and 1800s. The burning of fossil fuels produced acid rain which massively increased the reaction of water with the alkali Calcium Carbonate (limestone) which results in the erosion of the limestone.
Limestone (CaCO3) reacts with hydrogen ions in water. These are always present in water, since water undergoes autoprotolysis: H2O(l) = H+(aq) + OH-(aq) The more acidic the water is, the more limestone will react, and erode.
The erosion of marble sculpture and inscriptions exposed to the elements is one of the consequences of acid rain.
The equilibrium solubility of limestone (and marble) exposed to the atmosphere is dominated by the following reactions:
CaCO3(s) + H3O+(aq) = Ca2+(aq) + HCO3-(aq)
HCO3- + H3O+(aq) = CO2(aq) + 2 H2O(l)
H3O+(aq) + CO32-(aq) = HCO3-(aq) + H2O(l)
These reactions are responsible for the erosion of the marble and limestone
When originally used the limestone would generally be dressed (cut flat into blocks with a smooth surface). Over time the acid rain eats into the stone and exposes the interior of the rocks.
(Optional) Check out the bridge at the waypoint and see how much of the limestone has had to be replaced with modern bricks.
Head to the published coordinates. Stand at the centre of the west wall of the church beneath the window. At four feet up you will see some good examples of eroded limestone.
Question 1: What simple shape are these exposed fossils?
Still facing the wall, turn to your right and head around the corner. Again at 4 foot up, behind the trough, is a much darker limestone block that is also well eroded. These fossils are Crinoids.
Question 2: Describe what this particular example of Crinoids look like.
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