The Ancient Volcanoes of Great Britain, Volume 1 (of 2)

CHAPTER V. Underground Phases of Volcanic Action. B. Materials Injected or

Underground Phases of Volcanic Action. B. Materials injected or consolidated beneath the Surface--Intrusive Series: I. Vents of Eruption--i. Necks of Fragmentary Materials; ii. Necks of Lava-form Materials; iii. Distribution of Vents in relation to Geological Structure-Lines; iv. Metamorphism in and around Volcanic Cones, Solfataric Action; v. Inward Dip of Rocks towards Necks; vi. Influence of contemporaneous Denudation upon Volcanic Cones; vii. Stages in the History of old Volcanic Vents 52

CHAPTER VI. Underground Phases of Volcanic Action--_continued_. Ii.

Underground Phases of Volcanic Action--continued. II. Subterranean Movements of the Magma: i. Dykes and Veins; ii. Sills and Laccolites; iii. Bosses (Stocks, Culots), Conditions that govern the Intrusion of Molten Rock within the Terrestrial Crust 77

CHAPTER VII

Influence of Volcanic Rocks on the Scenery of the Land--Effects of Denudation 100

BOOK II

VOLCANIC ACTION IN PRE-CAMBRIAN TIME

CHAPTER VIII

Pre-Cambrian Volcanoes

The Beginnings of Geological History--Difficulties in fixing on a generally applicable Terminology--i. The Lewisian (Archæan) Gneiss; ii. The Dalradian or Younger Schists of Scotland; iii. The Gneisses and Schists of Anglesey; iv. The Uriconian Volcanoes; v. The Malvern Volcano; vi. The Charnwood Forest Volcano 109

BOOK III. The Cambrian Volcanoes

THE CAMBRIAN VOLCANOES

CHAPTER IX

Characteristics of the Cambrian System in Britain

The Physical Geography of the Cambrian Period--The Pioneers of Palæozoic Geology in Britain--Work of the Geological Survey in Wales--Subdivisions of the Cambrian System in Britain 139

CHAPTER X

The Cambrian Volcanoes of South Wales 145

CHAPTER XI

The Cambrian Volcanoes of North Wales, the Malvern Hills and Warwickshire 159

BOOK IV

THE SILURIAN VOLCANOES

CHAPTER XII

Characters of the Silurian System in Britain. The Arenig Volcanoes

The Land and Sea of Silurian time--Classification of the Silurian System--General Petrography of the Silurian Volcanic Rocks--I. The Eruptions of Arenig Age 173

CHAPTER XIII. The Eruptions of Llandeilo and Bala Age

The Eruptions of Llandeilo and Bala Age

i. The Builth Volcano--ii. The Volcanoes of Pembrokeshire--iii. The Caernarvonshire Volcanoes of the Bala Period--iv. The Volcanic District of the Berwyn Hills--v. The Volcanoes of Anglesey--vi. The Volcanoes of the Lake District; Arenig to close of Bala Period--vii. Upper Silurian (?) Volcanoes of Gloucestershire 202

CHAPTER XIV

The Silurian Volcanoes of Ireland 239

BOOK V

THE VOLCANOES OF DEVONIAN AND OLD RED SANDSTONE TIME

CHAPTER XV

The Devonian Volcanoes 257

CHAPTER XVI

The Volcanoes of the Old Red Sandstone

Geological Revolutions at the close of the Silurian Period Physical Geography of the Old Red Sandstone--Old Lake-basins, their Flora and Fauna--Abundance of Volcanoes--History of Investigation in the Subject 263

CHAPTER XVII. Distribution of the Volcanic Centres in the Lower Old Red

Distribution of the Volcanic Centres in the Lower Old Red Sandstone--Characters of the Materials Erupted by the Volcanoes 271

CHAPTER XVIII

Structure and Arrangement of the Lower Old Red Sandstone Volcanic Rocks in the Field 281

CHAPTER XIX

Volcanoes of the Lower Old Red Sandstone of "Lake Caledonia"

Description of the several Volcanic Districts: "Lake Caledonia," its Chains of Volcanoes--The Northern Chain: Montrose Group--Ochil and Sidlaw Hills--the Arran and Cantyre Centre--the Ulster Centre 294

CHAPTER XX. Volcanoes of the Lower Old Red Sandstone of

Volcanoes of the Lower Old Red Sandstone of "Lake Caledonia"--continued

The Southern Chain--The Pentland Volcano--The Biggar Centre--The Duneaton Centre--The Ayrshire Volcanoes 317

CHAPTER XXI. Volcanoes of the Lower Old Red Sandstone of the Cheviot Hills,

Volcanoes of the Lower Old Red Sandstone of the Cheviot Hills, Lorne, "Lake Orcadie" and Killarney 336

CHAPTER XXII

Volcanoes of the Upper Old Red Sandstone--The South-West of Ireland, the North of Scotland 348

BOOK VI

THE CARBONIFEROUS VOLCANOES

CHAPTER XXIII

The Carboniferous System of Britain and its Volcanic Records

Geography and Scenery of the Carboniferous Period--Range of Volcanic Eruptions during that time--I. The Carboniferous Volcanoes of Scotland--Distribution, Arrangement and Local Characters of the Carboniferous System in Scotland--Sketch of the Work of previous Observers in this Subject 355

CHAPTER XXIV. Carboniferous Volcanic Plateaux of Scotland

Carboniferous Volcanic Plateaux of Scotland

I. The Plateau-type restricted to Scotland--i. Distribution in the Different Areas of Eruption--ii. Nature of the Materials Erupted 367

CHAPTER XXV. Geological Structure of the Carboniferous Volcanic

Geological Structure of the Carboniferous Volcanic Plateaux of Scotland

1. Bedded Lavas and Tuffs; Upper Limits and Original Areas and Slopes of the Plateaux; 2. Vents; Necks of Agglomerate and Tuff; Necks of Massive Rock; Composite Necks; 3. Dykes and Sills; 4. Close of the Plateau-eruptions 383

CHAPTER XXVI. The Carboniferous Puys of Scotland

The Carboniferous Puys of Scotland

i. General Character and Distribution of the Puys; ii. Nature of the Materials Erupted--Lavas Ejected at the Surface--Intrusive Sheets--Necks and Dykes--Tuffs 414

CHAPTER XXVII. Geological Structure of the Carboniferous Puys of Scotland

Geological Structure of the Carboniferous Puys of Scotland

1. Vents: Relation of the Necks to the Rocks through which they rise--Evidence of the probable Subærial Character of some of the Cones or Puys of Tuff--Entombment of the Volcanic Cones and their Relation to the Superficial Ejections. 2. Bedded Tuffs and Lavas--Effects of Subsequent Dislocations. 3. Sills, Bosses, and Dykes 424

CHAPTER XXVIII. Illustrative Examples of the Carboniferous Puys of Scotland

Illustrative Examples of the Carboniferous Puys of Scotland

The Basin of the Firth of Forth--North Ayrshire--Liddesdale 462

LIST OF ILLUSTRATIONS

FIG. PAGE

1. Vesicular structure, Lava from Ascension Island, slightly less than natural size 15

2. Elongation and branching of steam-vesicles in a lava, Kilninian, Isle of Mull, a little less than natural size 17

3. Microlites of the Pitchstone of Arran (magnified 70 diameters) 19

4. Perlitic structure in Felsitic Glass, Isle of Mull (magnified) 19

5. Spherulitic structure (magnified) 19

6. Micropegmatitic or Granophyric structure in Granophyre, Mull (magnified) 20

7. Ophitic structure in Dolerite, Gortacloghan, Co. Derry (magnified) 20

8. Variolitic or orbicular structure, Napoleonite, Corsica (nat. size) 22

9. Flow-structure in Rhyolite, Antrim, slightly reduced 23

10. Lumpy, irregular trachytic lava-streams (Carboniferous), East Linton, Haddingtonshire 24

11. View at the entrance of the Svinofjord, Faroe Islands, illustrating the terraced forms assumed by basic lavas 25

12. Sack-like or pillow-form structure of basic lavas (Lower Silurian), Bennan Head, Ballantrae, Ayrshire 26

13. Alternations of coarser and finer Tuff 34

14. Alternations of Tuff with non-volcanic sediment 35

15. Ejected block of basalt which has fallen among Carboniferous shales and limestones, shore, Pettycur, Fife 37

16. Effects of denudation on a Vesuvian cone 40

17. Section to illustrate the structure of the Plateau type 43

18. Diagram illustrating the structure and denudation of Puys 45

19. Section illustrating submarine eruptions; alternations of lavas and tuffs with limestones and shales full of marine organisms 48

20. Diagram illustrating volcanic eruptions on a river-plain 49

21. Diagram illustrating volcanic eruptions on a land-surface 50

22. Ground-plans of some volcanic vents from the Carboniferous districts of Scotland 55

23. View of an old volcanic "Neck" (The Knock, Largs, Ayrshire, a vent of Lower Carboniferous age) 56

24. Section of neck of agglomerate, rising through sandstones and shales 58

25. Neck filled with stratified tuff 64

26. Section of neck of agglomerate with plug of lava 65

27. Section of agglomerate neck with dykes and veins 66

28. Section of neck filled with massive rock 68

29. Successive shiftings of vents giving rise to double or triple cones 70

30. Section to show the connection of a neck with a cone and surrounding bedded tuffs 71

31. Diagram illustrating the gradual emergence of buried volcanic cones through the influence of prolonged denudation 75

32. Dyke, Vein, and Sill 80

33. Section of Sill or Intrusive Sheet 83

34. Ideal section of three Laccolites. (After Mr. Gilbert) 86

35. Diagram illustrating the stratigraphical relations of the pre-Cambrian and Cambrian rocks of the North-west Highlands of Scotland 112

36. Map of a portion of the Lewisian gneiss of Ross-shire 118

37. Section showing the position of sills in the mica-schist series between Loch Tay and Amulree 124

38. Sketch of crushed basic igneous rock among the schists, E. side of Porth-tywyn-mawr, E. side of Holyhead Straits 128

39. Section across the Uriconian series of Caer Caradoc 132

40. Map of the volcanic district of St. David's 146

41. Section showing the interstratification of tuff and conglomerate above Lower Mill, St. David's 154

42. Basic dyke traversing quartz-porphyry and converted into a kind of slate by cleavage. West side of Llyn Padarn 162

43. Section of well-cleaved tuff, grit and breccia passing up into rudely-cleaved conglomerate and well-bedded cleaved fine conglomerate and grit. East side of Llyn Padarn 163

44. Section of Clegyr on the north-east side of Llyn Padarn, near the lower end 164

45. Section across the Cambrian formations of the Malvern Hills, showing the position of the intercalated igneous rocks. After Phillips 170

46. Section across Rhobell Fawr 178

47. Section at the Slate Quarry, Penrhyn Gwyn, north slopes of Cader Idris 180

48. Sketch-section across Cader Idris 182

49. Section across the Moelwyn Range 185

50. Section across the anticline of Corndon 190

51. Structure in finely-amygdaloidal diabase lava, south of mouth of Stinchar River, Ayrshire 193

52. View of Knockdolian Hill from the east 194

53. Section across the Lower Silurian volcanic series in the south of Ayrshire (B. N. Peach) 197

54. Section of part of the Arenig volcanic group, stream south of Bennane Head, Ayrshire 198

55. Flow-structure in the lowest felsite on the track from Llanberis to the top of Snowdon 211

56. Section of Snowdon 212

57. Section across the Berwyn Hills. (Reduced from Horizontal Section, Geol. Surv. Sheet 35) 219

58. Section of the strata on the shore at Porth Wen, west of Amlwch 223

59. Section of intercalated black shale in the volcanic series at Porth yr hwch, south of Carmel Point, Anglesey 224

60. Green slates overlain with volcanic breccia, Carmel Point 224

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