T he significance of the outliers of Cretaceous and later age resting on the Palæozoic strata of Devon and Cornwall has been frequently noted, especially with reference to the evidence yielded by them of the extent of the great marine transgressions. The details of their petrology, considered in relation to their present altitude and geographical location, are dealt with in this communication, and an attempt is made to throw light on the conditions of their deposition and the source of their constituents. Lying as they do, around and among some of the most important igneous masses in the country, they may be expected to afford evidence regarding the stability of detrital minerals and of the source of constituents in sediments of the same age, but of wider geographical distribution. A comparison of the petrography of these outliers with that of the Greensand, Eocene, and Pliocene strata farther east has therefore been instituted. These outliers in the West Country may be grouped thus :— Cretaceous (Upper Greensand). Great Haldon Hills (Devon). Little Haldon Hills (Devon). Eocene (? Bagshot). (?) Marazion, near Penzance (Cornwall). Buckland Brewer, near Bideford (Devon). Great Haldon Hills. Little Haldon Hills. Oligocene (Aquitanian). Petrockstrow, near Torrington (Devon). Bovey Tracey and Newton Abbot (Devot). Pliocene. St. Erth and Lelant (Cornwall). Crouza Down, near St. Keverne (Cornwall). St. Agnes (Cornwall), together with certain deposits age (see p. 223). The respective heights of the upper and lower surfaces of the deposits above Ordnance-datum are as follows :— II. E vidence