“ The Carboniferous rocks of the Cumbrae belong to the lower part of the Calciferous Sandstone series with the accompanying volcanic zone. In the larger island these sediments, comprising sandstones, red, purple and mottled clays with occasional bands of nodular limestone or cornstone, occupy a considerable area on the north side of Millport Bay. In the Little Cumbrae they appear on the east side, where they underlie and are interbedded with the lavas. The interesting geological feature of these islands is the development of Lower Carboniferous volcanic rocks. ”

“ Next come dikes of olivine basalt of the type of the Lion’s Haunch on Arthur’s Seat, which, though possessing the same general trend as the trachytes, are seen to cut them. The members of the third group comprise dikes of dolerite or basalt with or without olivine, which have a general east and west trend, and as they intersect the two previous groups they must be of later date. They probably belong to the east and west quartz dolerite dikes which are now referred to late Carboniferous time. Lastly there are representatives of the basalt dikes of Tertiary age with a north-west trend. ”

“ The flows are often scoriaceous at the top and sometimes display columnar structure, as in the crags at the lighthouse. Those rocks examined microscopically consist of basalts which are often porphyritic. In Great Cumbrae the intrusive rocks mark four periods of eruption, three of which may be of Carboniferous age. The oldest, consisting of trachytes, occur as sheets and dikes trending generally E.N.E., and are confined chiefly to the Upper Old Red Sandstone. ”