Dolostone on the fault near Barns Ness

This is the shore at Barns Ness near Dunbar on the Edinburgh coastline. It has an impressive display of sedimentary rocks including one of the biggest limestone outcrops in the Scottish lowlands. We used a geology leaflet to find our way around http://www.edinburghgeolsoc.org/downloads/rigsleaflet_barnsnessa4.pdf 

In picture below, there is a crack in the rock in the middle of the foreground which lines up with the lumps of rock in the distance. It's a geological fault where earth movements have split the rock.

 The rocks below are examples of breccias. The original rock is fractured by the earth movements. This creates cracks. Mineral bearing liquids flow into the cracks. The water evaporates and the minerals crystalise out. The edges of the broken fragments are still sharp and jagged, showing that there was no transportation to cause erosion. In other words, they are still in the place that the fracture took place.

The leaflet says that this is dolostone. This will have formed because the inflowing mineral had more magnesium in it that normal limestone and so changed the chemical composition. I think that the dolostone must be harder than ordinary limestone because it has remained as the big lumps sticking out marking the faultline clearly.