Exposures along the coast show rocks which are tilted and folded. The rocks are called greywackes are made of mud, silt and sandstones which formed at the edge of the Iapetus ocean basin. Geologists know they formed under water because of structures found in the rocks. One feature is that the fragments of rock from which they are made are well sorted. The larger, heavier bits sank quickly while the finer bits took longer to settle to the bottom.
Nearby rocks contain marine fossils called graptolites which floated in the ocean.
Originally the greywackes were laid down horizontally, but today show spectacular folds. These folded rocks are found over many tens of kilometres. Large scale mountain building forces. These forces buckled and rucked the greywackes as the continents came together. The final evidence comes from the composition of the Scottish rocks - they match those found in Newfoundland today.