The small amount of geophysics done, and occasional building-related exposures, combined with small exposures in the banks of the River Don, suggest that it is actually sited on an inlier of Devonian "Old Red" sandstones and silts. The outskirts of the city spread beyond the (inferred) limits of the outlier onto the surrounding metamorphic/ igneous complexes formed during the Dalradian period (approximately 480–600 million years ago) with sporadic areas of igneous Diorite granites to be found, such as that at the Rubislaw quarry which was used to build much of the Victorian parts of the city.