[Footnote 90: The rocks are shown in Sheets 9, 14 and 15 of the Geological Survey of Scotland, to which, and their accompanying Explanations, reference is made. The Ayrshire basin was mapped by me, the necks in the Dalmellington ground by Mr. James Geikie, the Nithsdale area by Mr. R. L. Jack, Mr. H. Skae and myself.] The materials erupted by the Scottish Permian volcanoes display a very limited petrographical range, contrasting strongly in this respect with the ejections of all the previous geological periods. They consist of lavas generally more or less basic, and often much decayed at the surface; and of agglomerates and tuffs derived from the explosion of the same lavas. The lavas are dull reddish or purplish-grey to brown or almost black rocks; sometimes compact and porphyritic, but more usually strongly amygdaloidal, the vesicles have been filled up with calcite, zeolites or other infiltration. The porphyritic minerals are in large measure dull red earthy pseudomorphs of hæmatite, in many cases after olivine. These rocks have not yet been fully studied in regard to their composition and microscopic structure. A few slides, prepared from specimens collected in Ayrshire and Nithsdale, examined by Dr. Hatch, were found to present remarkably basic characters. One from Mauchline Hill is a picrite, composed chiefly of olivine and augite, with a little striped felspar. Others from the Thornhill basin in Dumfriesshire show an absence of olivine, and sometimes even of augite. The rock of Morton Castle consists of large crystals of augite and numerous grains of magnetite in a felspathic groundmass full of magnetite. Around Thornhill are magnetite-felspar rocks, composed sometimes of granular magnetite with interstitial felspar. Throughout all the rocks there has been a prevalent oxidation of the magnetite, with a consequent reddening of the masses. The pyroclastic materials consist of unstratified agglomerates and tuffs, generally found in necks, and of stratified tuffs, which more or less mingled with non-volcanic material, especially red sandstone, are intercalated among the bedded lavas or overlie them, and pass upward into the ordinary Permian red sandstones.