English: Road Cutting The rock faces exposed when the new A838 was built have become a mecca for geologists because they show the relationships of the different types of rock in the Lewisian. The oldest rock is the striped grey Badcallian gneiss, which is 2700 to 3000 million years old. Between 2400 and 2200 million years ago these grey rocks were intruded by dykes of black igneous rock, known as Scourie dykes. These rocks were later deformed and again intruded by coarse pink granites and pegmatites, themselves deformed during the Laxfordian event of 1900 to 1700 million years ago.