The igneous rocks of the Mountsorrel area, by reason of their accessibility and economic value, have attracted the attention of geologists since the middle of last century. The latest and most comprehensive account of the district is that of E. E. Lowe (1) and at the end of the paper a useful bibliography of earlier publications is given. Additional notes are to be found in the pamphlet published for the visit of the Geologists' Association to Charnwood Forest in 1928, including a structural study of the Mountsorrel “granite” by F. Jones (2).

The following notes refer to a collection of rock specimens made by the late Capt. T. Alex. Barns, F.R.G.S. Along with a summary of the geology of the four main islands in the Gulf of Guinea by the late Prof. J. W. Gregory it was intended to publish them as an appendix to a travel book by Capt. Barns. This book was never published as Capt. Barns was killed at Chicago in a motor accident on the 5th March, 1930. He had, however, already published an account of his journeys in the Geographical Journal. Prof. Gregory's manuscript on the geology of the islands cannot now be found. It is felt, however, that the petrographical notes and the two new chemical analyses that accompany them, should be placed on record.

The ancient rocks of Leicestershire may be taken to comprise the pre-Cambrian volcanic and sedimentary rocks of Charnwood Forest, and the igneous rocks intrusive into them, viz. the dacite-porphyrites of Bardon Hill, Peldar, and High Sharpley, etc., the granophyric diorites and porphyrites within and south-west of the Forest and in South Leicestershire, and the Mountsorrel granite or granodiorite. There is reason to believe that all except the last are pre-Cambrian in age: for the last a post-Silurian age seems most probable. These ancient rocks are now exposed through the removal of the Keuper Marl, whichhad largely if not completely buried them. In glacial times, however, small areas have been reburied under glacial deposits.

In a recent paper the author attempted to explain something of the mechanism of contamination in acid magmas, but nothing was said about the tendency, of contamination to produce normal rock types. It is to repair this deficiency that the present communication is presented.