rock will be again referred to in connection with the vent from which its materials were probably derived. As in the case of the agglomerates of the vents, pieces of older acid lavas, and still more of the non-volcanic rocks that underlie the plateaux, are found in the bedded conglomerates and breccias. In Antrim and Mull, for instance, fragments of flint and chalk are of common occurrence. A characteristic example of this kind of rock forms the platform of the columnar bed out of which Fingal's Cave, Staffa, has been excavated (Fig. 266_a_). ([Greek: beta]) Felsitic Breccia.--This variety, though of rare occurrence, is to be seen in a number of localities in the island of Mull. It is composed in great measure of angular fragments of close-grained flinty felsitic or rhyolitic rocks, sometimes showing beautiful flow-structure, together with pieces of quartzite and amygdaloidal basalt, the dull dirty-green matrix appearing to be made up chiefly of basalt-dust. ([Greek: gamma]) Rhyolitic Conglomerate.--Between the upper and lower group of basalts in the Antrim plateau there occur bands of a pale fawn-coloured conglomerate largely made up of more or less rounded fragments of rhyolite, like some of the varieties of the rock which occur in place on the plateau. The rhyolitic debris is often mixed with pebbles of basalt. Sometimes it becomes so fine as to pass into pale clays. ([Greek: delta]) Breccias of non-volcanic materials.--These, the most exceptional of all the fragmentary intercalations in the plateaux, consist almost wholly of angular blocks of rocks which are known to underlie the basalts, but with a variable admixture of basalt fragments. They are due to volcanic explosions which shattered the subjacent older crust of rocks, and discharged fragments of these from the vents or allowed them to be borne upwards on an ascending column of lava. Pieces of the non-volcanic platform are of common occurrence among the fragmentary accumulations, especially in the lower parts of the plateaux basalts. But I have never seen so remarkable an example of a breccia of this kind as that which occurs near the summit of Sgurr Dearg, in the south-east of Mull. The bedded basalt encloses a lenticular band of exceedingly coarse breccia, consisting mainly of angular pieces of quartzite, with fragments of amygdaloidal basalt. In the midst of the breccia lies a huge mass or cake of erupted mica-schist, at least 100 yards long by 30 yards wide, as measured across the strike up the slope of the hill. To the west, owing to the thinning out of the breccia, this piece of schist comes to lie between two beds of basalt. A little higher up, other smaller but still large blocks of similar schist are involved in the basalt, as shown in Fig. 262. As the huge cake of mica-schist plunges into the hill, its whole dimensions cannot be seen; but there are visible, at least, 15,000 cubic yards, which must weigh more than 30,000 tons. Blocks of