The chief geological investigation of the last decade of his life was devoted to the Highlands of Scotland, where he wrongly believed he had succeeded in showing that the vast masses of crystalline schists, previously supposed to be part of what used to be termed the Primitive formations, were really not older than the Silurian period, for that underneath them lay beds of limestone and quartzite containing Lower Silurian (Cambrian) fossils. James Nicol recognised the fallacy in the Murchison's extant theory and propounded his own ideas, in the 1880s these were superseded by the correct theory of Charles Lapworth, which was corroborated by Benjamin Peach and John Horne.