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

186. Section of intercalated dark limestone, shale and chert in the tuff south of Poyll Vaaish Bay, Isle of Man 26

187. Section of part of a volcanic neck on shore to the south-east of Poyll Vaaish Bay, Isle of Man 29

188. Section of successive discharges and disturbances within a volcanic vent. Scarlet Point, Isle of Man 29

189. Section of dyke and sill in the tuffs west of Scarlet Point, Isle of Man 30

190. Section on south side of vesicular sill west of Scarlet Point 31

191. Bands of vesicles in the same sill 31

192. Croghan Hill, King's County, from S.S.W. 38

193. Section in quarry on roadside east of Limerick, close to viaduct of the Limerick and Erris Railway 44

194. Section of the volcanic escarpment, east of Shehan's Cross-roads, south of Limerick 45

195. View of Derk Hill, a volcanic neck on the south side of the Limerick basin 47

196. Section across the Limerick volcanic basin 48

197. Section of a bed of volcanic breccia in the Carboniferous Slate; White Bull Head, County Cork 50

198. Volcanic breccia invading and enclosing Carboniferous slate, White Bull Head 50

199. General section across the Permian basin of Ayrshire 59

200. Section of lavas, east side of Mauchline Hill 60

201. Section of the top of the volcanic series near Eastside Cottage, Carron Water, Nithsdale 60

202. Section of two outliers of the Permian volcanic series at the foot of Windyhill Burn, Water of Ae, Dumfriesshire 61

203. The Green Hill, Waterside, Dalmellington, from the south; a tuff-neck of Permian age 62

204. Patna Hill from the Doon Bridge, Ayrshire; a tuff-neck of Permian age 63

205. Ground plans of Permian volcanic vents from the Ayrshire Coal-field. On the scale of six inches to a mile 64

206. Section of sills traversing the Permian volcanic series. River Ayr, Ballochmyle 66

207. Section showing the relations of the later rocks of Arthur Seat 68

208. Section in brooks between Bonny town and Baldastard, Largo 70

209. View of Largo Law from the east 71

210. View of small neck in Calciferous Sandstones, on the shore, three miles east from St. Andrews 72

211. Ground-plan of Permian volcanic vents 73

212. Small neck in Calciferous Sandstones a little east from the "Rock and Spindle," two and a half miles east from St. Andrews 74

213. Plan of volcanic necks at Kellie Law, East of Fife, on the scale of three inches to one mile 75

214. Plan of the craters in Volcanello, Lipari Islands 75

215. Section of the strata at the edge of the volcanic vent on the east side of Elie Harbour 76

216. Agglomerate of neck on shore at Ardross, two miles east from Elie 77

217. Ground-plan of volcanic neck, Elie Harbour, showing circular disposition of the stratification 80

218. Section across the great vent of Kincraig, Elie, on a true scale, vertical and horizontal, of six inches to a mile 81

219. Dyke in volcanic neck, on the beach, St. Monans 82

220. Section of part of crater rim, Island of Volcano 83

221. Dyke rising through the agglomerate of a volcanic vent; Kincraig, Elie 84

222. Radiating columnar dyke in the tuff of a volcanic vent. Rock and Spindle, two and a half miles east from St. Andrews 86

223. View of part of the shore front of the great vent at Kincraig, looking westward, with the columnar basalt in front 88

224. Plan of volcanic neck on beach near St. Monans 89

225. Columnar basalt in the neck of Kincraig, Elie, seen from the west 90

226. Section across Largo Law 91

227. Vein of "white-trap" cutting black carbonaceous shales, a little west from St. Monans Church 92

228. Section at Belvedere, S. W. of Exeter 97

229. Diagram to show the unconformability and overlap of the Permian rocks in the Crediton Valley 97

230. Section of the volcanic series at Kellerton, Devonshire 98

231. Section of agglomerate overlain with sandstone and andesite, Posbury, Crediton 99

232. Diagrammatic section across Titterstone Clee Hill 102

233. Dyke on the south-east coast of the Island of Mull 119

234. Fissure left by the weathering out of a dyke 120

235. Plan of basalt-veins with selvages of black basalt-glass, east side of Beinn Tighe, Isle of Eigg 126

236. Arrangement of lines of amygdales in a dyke, Strathmore, Skye 130

237. Systems of joints in the dykes 132

238. Section of cylindrical vein or dyke, cutting the bedded lavas, east side of Fuglö, Faroe Islands 133

239. Joint-structures in the central vitreous portion of the Eskdale Dyke (B. N. Peach) 133

240. Microscopic structure of the vitreous part of the Eskdale Dyke 136

241. Section along the line of the Cleveland Dyke at Cliff Ridge, Guisbrough (G. Barrow), scale, 12 inches to 1 mile 147

242. Section along the course of the Cleveland Dyke, at the head of Lonsdale, Yorkshire (G. Barrow, in the _Memoirs of the Geol. Survey_, Geology of Cleveland, p. 61) 148

243. Section across the extreme upper limit of Cleveland Dyke, on the scale of 20 feet to one inch (Mr. G. Barrow) 149

244. Upper limit of Cleveland Dyke in quarry near Cockfield (after Mr. Teall) 149

245. Section along the course of the Cleveland Dyke across the Cross Fell escarpment (scale of one inch to one mile) 150

246. Branching portion of the great dyke near Hawick (length about one mile) 153

247. Branching dyke at foot of Glen Artney (length about four miles) 153

248. Basic veins traversing Secondary limestone and sandstone on the coast cliffs, Aidnamurchan 155

249. Section showing the connection of a Dyke with an Intrusive Sheet, Point of Suisnish, Skye 156

250. Section to show the connection of a Dyke with an Intrusive Sheet, Stirlingshire Coal-field 157

251. Intersection of dykes in bedded basalt, Calliach Point, Mull 158

252. Basalt veins traversing bedded dolerites, Kildonan, Eigg 159

253. Ground-plan of intersecting dykes in Lias limestone, Shore, Harrabol, East of Broadford, Skye 159

254. Compound dyke, Market Stance, Broadford, Skye 162

255. Section of coal rendered columnar by intrusive basalt, shore, Saltcoats, Ayrshire 164

256. Dolerite dyke with marginal bands of "white trap," in black shale, Lower Lias, Pabba 166

257. Map of the chief dykes between Lochs Ridden and Striven (C. T. Clough, Geological Survey, Sheet 29) 170

258. Basalt-veins traversing granophyre, St. Kilda 173

259. Section of scoriaceous and prismatic basalt, Camas Tharbernish, north shore of Canna Island 187

260. Banded amygdaloidal basalt showing layers of elongated and steeply inclined vesicles, Macleod's Maidens, Skye 191

261. Termination of basalt-beds, Carsaig, Mull 193

262. Breccia and blocks of mica-schist, quartzite, etc., lying between bedded basalts, Isle of Mull 197

263. Section of Knocklayd, an outlier of the Antrim basalt-plateau lying on Chalk 202

264. Diagram-Section of the Antrim Plateau 203

265. View Of Basalt escarpment, Giant's Causeway, with the Amphitheatre and Chimneys. (From a photograph by Mr. R. Welch) 207

266. Basalt-capping on the top of Ben Iadain, Morven 209

266_a_. View of the south side of Staffa, showing the bedded and columnar structure of the basalt 210

267. View of Rum from the harbour of Canna 216

268. Section of the cliffs below Compass Hill, Isle of Canna 218

269. Lava cutting out conglomerate and shale. Shore below Canna House 224

270. Section of shales and tuffs, with a coniferous stump lying between two basalt-sheets, Cùl nam Marbh, Canna 225

271. Dùn Mòr, Sanday. (From a photograph by Miss Thom) 226

272. View of the Dùn Beag, Sanday, seen from the south. (From a Photograph by Miss Thom) 230

273. View of Dùn Beag, Sanday, from the north. The island of Rum in the distance. (From a Photograph by Miss Thom) 231

274. Section of eastern front of Dùn Beag 232

275. Enlarged section on the western side of Dùn Beag 233

276. Geological map of the Island of Eigg 235

277. Section of the geological structure of the Island of Eigg 236

278. View of the Scuir of Eigg from the east 237

279. Natural section at the cliff of Bideann Boidheach, north-west end of the Scuir of Eigg 239

280. View of the Scuir of Eigg from the south 242

281. View of the Scuir of Eigg from the south-west of the Loch a Bhealaich, showing the bedded character of the mass 243

282. Section at the base of the Scuir of Eigg (east end) 244

283. Terraced hills of basalt plateau (Macleod's Tables), Skye 250

284. "Macleod's Maidens" and part of basalt cliffs of Skye 251

285. Intercalated group of strata between Basalts, An Ceannaich, western side of Skye 252

286. Escarpment of Plateau-basalts, Cliffs of Talisker, Skye 253

287. Section of the largest of Macleod's Maidens 254

288. Dying out of lava-beds, east side of Sandö, Faroe Isles 257

289. Lenticular lavas, western front of Hestö, Faroe Isles 257

290. Lenticular lavas, east side of Svinö, Faroe Isles 258

291. Section at Frodbonyp, Suderö, Faroe 258

292. Fissure (gjá) in a lava-field, Iceland. (From a photograph by Dr. Tempest Anderson) 262

293. Cones on the great Laki fissure, Iceland. (From a photograph by Dr. Tempest Anderson) 263

293_a_. Plan of small craters along the line of great Laki fissure, Iceland. (After Mr. Helland, reduced) 264

294. Slemish, a volcanic neck or vent on the Antrim plateau, seen from the north 272

295. Section of volcanic vent at Carnmony Hill (E. Hull) 272

296. Section of the east side of Scawt Hill, near Glenarm 273

297. Section of Neck of basalt, Bendoo, Ballintoy 273

298. Volcanic Neck of dolerite near Cushendall 274

299. Section of Volcanic Neck at 'S Airde Beinne, near Tobermory, Mull 274

300. Interior of the Volcanic Neck of 'S Airde Beinne, near Tobermory, Mull 275

301. Diagram to show the probable relation of the Neck at Carrick-a-raide, Antrim, to an adjacent group of tuffs 277

302. Section of agglomerate Neck at Maclean's Nose, Ardnamurchan 279

303. Diagram to show the probable relations of the rocks on the southern flank of Beinn Dearg Bheag 282

304. Section of Volcanic Vent and connected lavas and tuffs, Scorr, Camas Garbh, Portree Bay, Skye 284

305. Section of the Volcanic Series at Ach na Hannait, south of Portree, Skye 288

306. View of part of a Volcanic Neck at the eastern end of the island of Canna. (From a photograph by Miss Thom) 289

307. Columnar Basalt invading agglomerate of Volcanic Vent, Coroghon Mòr, Isle of Canna. (Height above 20 feet) 291

308. Columnar Basalt invading Volcanic conglomerate, north side of Alman Islet, Canna 291

309. View of neck-like mass of breccia, Brochel, Raasay 292

310. View of Volcanic Neck piercing and overlain by the Plateau-Basalts, Stromö, entrance of Vaagöfjord, Faroe Islands. (From a photograph by Colonel Evans) 294

311. Section of the same Neck as that shown in Fig. 310 295

312. Volcanic Neck close to that shown in Figs. 310 and 311 296

313. Section of wall of another Neck of agglomerate in the same group with those represented in Figs. 310, 311, and 312 296

314. View of "Segregation-Veins" in a dolerite sill, Portrush, Antrim 300

315. View of Fair Head, from the east, showing the main upper sill and a thinner sheet cropping out along the talus 301

316. View of Fair Head from the shore. (From a photograph by Mr. R. Welch) 302

317. Section at Farragandoo cliff, west end of Fair Head, showing the rapid splitting up and dying out of an Intrusive Sheet slope 304

318. View of the Trotternish Coast, showing the position of the band of Sills 305

319. Columnar Sill intrusive in Jurassic Strata east of Kilmartin, Trotternish, Skye 306

320. View of the northern precipice (500 feet high) of the largest of the Shiant Isles. (From a photograph by Colonel Evans) 308

321. Section of thin Intrusive Sheets and Veins in carbonaceous shales lying among the Plateau-basalts, cliffs north of Ach na Hannait, between Portree Bay and Loch Sligachan 311

322. Upper part of Sill, Moonen Bay, Waternish, Skye, showing the divergence of veins 313

323. Section of the base of the Basalt-plateau with sill and dykes, Sound of Soa, Skye 314

324. Section of Dolerite Sill cut by another sill, both being traversed by dykes, Rudh' an Iasgaich, western side of Sleat, Skye 316

325. Section to show Bedded and Intrusive Sheets, Eigg 318

326. Ground plan of Sills at Ben Hiant, Ardnamurchan. 321

327. Section of two Sills in schistose grits, west end of Beinn na h-Urchrach, Ardnamurchan 322

328. Sill traversing bedded Basalts, cliffs of Stromö, at entrance of Vaagöfjord 323

329. View of the same Sill seen from the channel opposite the island of Kolter 324

330. Granulitic and coarsely foliated Gabbro traversed by later veins of felspathic Gabbro, Druim an Eidhne, Cuillin Hills, Skye 331

331. Scuir na Gillean, Cuillin Hills, showing the characteristic craggy forms of the Gabbro. (From a photograph by Mr. Abraham, Keswick) 335

332. Section across Glen Brittle, to show the general relations of the Bedded Basalts and the Gabbros 336

333. View of the crest of the Cuillin Hills, showing the weathering of the Gabbro along its joints and of a compound basic dyke which rises through it. (From a photograph by Mr. Abraham, Keswick) 338

334. Section across the Coire Uaigneich, Skye 341

335. Banded and puckered gabbro, Druim an Eidhne, Glen Sligachan, Skye 342

336. Banded structure in the Gabbro, from the ridge of Druim an Eidhne, between Loch Coruisk and Glen Sligachan 343

337. Banded and doubly folded Gabbro, Druim an Eidhne, 10 feet broad 345

338. Sketch of banded structure in the Gabbros of the hills at the head of Loch Scavaig 347

339. Outline of the hills of the Island of Rum, sketched from near the Isle of Eigg 350

340. View of Allival, Rum, sketched from the base of the north-east side of the cone 352

341. Section of foliated Gabbros in the Tertiary volcanic series of Allival, Rum 353

342. Altered Plateau-Basalts invaded by Gabbro, and with a Dyke of prismatic Basalt cutting both rocks, north slope of Ben Buy, Mull 357

343. Theoretical representation of the structure of one of the Gabbro bosses of the Inner Hebrides 362

344. Section through the Puy de la Goutte and Puy de Chopine 374

345. View of the Huche Pointue and Huche Platte west of Le Pertuis 376

346. View of Glamich, 2537 feet, Glen Sligachan. (From a photograph by R. J. A. Berry, M.D., lent by the Scottish Mountaineering Club) 380

347. Section across the north slope of Beinn an Dubhaich, Skye 383

348. Section from Beinn Dearg to Beinn an Dubhaich, Skye 385

349. Section at north end of Beinn na Cro, Skye 388

350. Ground-plan of basic dyke in Cambrian limestones truncated by granophyre which encloses large blocks of the dyke, Torrin, Skye 393

351. Section on south side of Beinn an Dubhaich, Skye, showing the truncation of a basalt-dyke 394

352. View of the hills on the south side of the head of Loch na Keal, showing the junction of the Granophyre and the bedded basalts 396

353. Section on south side of Cruach Tòrr an Lochain, Mull 398

354. Section at head of Allt na Searmoin, Mull 398

355. Section on south side of Beinn Fhada, Mull 399

356. Section to south of Loch na Dàiridh, Mull 400

357. Section of junction of south side of Loch Ba' Granophyre boss, with the bedded basalts, Mull 401

358. Mass of dark gabbro about two feet in diameter traversed by pale veins of Granophyre, lying on north slope of Creag na h-Iolaire, Mull 402

359. Section at Creag na h-Iolaire, Glen More, Mull, showing basalts and gabbros resting on and pierced by Granophyre 402

360. Section on north side of Orval, Rum 404

361. Junction of Quartz-porphyry (Microgranite) and basic rocks, south-east side of Orval, Rum 404

362. Junction of Granophyre and gabbro, north side of St. Kilda 410

363. Veins of Granophyre traversing gabbro and splitting up into thin threads, north side of St. Kilda 411

364. Pale Granophyre injected into dark basalt, South Bay, St. Kilda 412

365. Veins of Granophyre traversing a fine-grained gabbro and scarcely entering a coarse-grained sheet, west side of Rueval, St. Kilda 413

366. View of sills and veins of pale Granophyre traversing sheets of gabbro, west side of St. Kilda. (From a photograph by Colonel Evans) 414

367. Section of the sea-cliff below Conacher, St. Kilda, showing basic dykes in Granophyre 417

368. Triple basic dyke, sea-cliff, east side of St. Kilda 417

369. Jointed structure of the Granite near the top of Goatfell, Arran. (From a photograph by Mr. W. Douglas, lent by the Scottish Mountaineering Club) 419

370. Intrusive Rhyolite in the lower basalt group of Antrim, Templepatrick 427

371. Section across the southern slope of Carnearny Hill, Antrim 427

372. Section across the Granophyre Sills at Loch a' Mhullaich, above Skulamus, Skye 433

373. Section to show the connection of a sill of Granophyre with its probable funnel of supply, Raasay 436

374. Granophyre sill resting on Lower Lias shales with a dyke of basalt passing laterally into a sill, Suisnish Point, Isle of Raasay 436

375. Weathered surface of spherulitic Granophyre from dyke in banded gabbros, Druim an Eidhne, Meall Dearg, Glen Sligachan, Skye. Natural size 438

376. Plan of portion of the ridge north of Druim an Eidhne, Glen Sligachan, Skye, showing three dykes issuing from a mass of Granophyre 439

377. Weathered surface of spherulitic Granophyre, from dyke in banded gabbros, Druim an Eidhne, Meall Dearg, Glen Sligachan, Skye. Natural size 440

378. Plan of pale Granophyric dyke, with spherulitic and flow-structure, cutting and enclosing dark gabbro, Druim an Eidhne 441

379. Dyke (six to ten feet broad) proceeding from a large body of Granophyre and traversing gabbro, from the same locality as Figs. 375 and 377 442

380. Section of intruded veins of various acid rocks above River Clachaig, Mull 443

381. Pitchstone vein traversing the bedded basalts, Rudh an Tangairt, Eigg 445

382. Reversed fault on the eastern side of Svinö, Faroe Isles 454

383. Reversed fault on the north-east headland of Sandö, Faroe Isle 454

MAPS

V. Map of the Permian volcanic districts of Scotland _To face p._ 106

VI. Map of the Tertiary volcanic region of the West of Scotland _To face p._ 296

VII. Map of the Tertiary volcanic district of the North-East of Ireland _To face p._ 446