The Bosses and Sheets of Gabbro in the Districts of Rum, Ardnamurchan, Mull, St. Kilda and North-East Ireland. History of the Gabbro Intrusions 349 CHAPTER XLV The Acid Rocks Their Petrography--Their Stratigraphical Position and its Analogies in Central France 364 CHAPTER XLVI Types of Structure in the Acid Rocks--Bosses 378 CHAPTER XLVII The Acid Bosses of Mull, Small Isles, St. Kilda, Arran, and the North-East of Ireland 395 CHAPTER XLVIII The Acid Sills, Dykes and Veins 430 CHAPTER XLIX The Subsidences and Dislocations of the Plateaux 447 CHAPTER L Effects of Denudation 455 CHAPTER LI Summary and General Deductions 466 LIST OF ILLUSTRATIONS FIG. PAGE 176. Section from the great Limestone escarpment on the west to the Millstone Grit hills east of Teesdale 4 177. Sections of the Carboniferous Limestone series of Northumberland showing the variations in the position of the Whin Sill. By Messrs. Topley and Lebour 6 178. View of two volcanic necks in the Carboniferous Limestone series, at Grange Mill, five miles west of Matlock Bath, from the north 14 179. Plan of necks and bedded tuff at Grange Mill, five miles west of Matlock Bath 15 180. Section across the smaller volcanic neck and the stratified tuff in Carboniferous Limestone, Grange Mill 15 181. Section of vesicular and amygdaloidal diabase resting on Carboniferous Limestone, Peak Forest Limeworks, Great Rocks Quarry 19 182. View of the superposition of Carboniferous Limestone upon toadstone, Raven's Tor, Millersdale (length about 100 feet) 19 183. Section at lime-kiln, south of Viaduct, Millersdale Station 20 184. Limestones passing under stratified tuffs, Poyll Vaaish, Isle of Man 24 185. Section of tuff, showing intercalations of black impure chert, west of Closenychollagh Point, near Castletown, Isle of Man 25