Part 2. The Mona Complex

Chapter 3 — Introduction to the Mona Complex

Regions and Inliers. Composition, Characters, and Sub-divisions. The Designation 'Mona Complex'.

Chapter 4 — The petrology of the Mona Complex

Introductory.

The Holyhead Quartzite.

The South Stack Series: The South Stack Series Proper. The Coeden Beds.

The New Harbour Group: The Green-mica-schists. Green Biotite. The Amlwch Beds. The Jaspery Phyllites. The Bedded Jaspers. The Spilitic Lavas.

The Skerries Group: The Church Bay Tuffs. The Skerries Grits. Their Conglomerates. The Tyfry Beds.

The Gwna Group: The Alternating Grit and Phyllite. Autoclastic Phyllite-and-Grit Mélange. The Gwna Green-schist. The Spilitic Lavas. The Tuffs. The Albite-Diabases. Kerato-phyre. Basic Schists. The Quartzites. The Limestones. Graphitic Phyllite. The Jaspers. The Jaspery Phyllites.

The Fydlyn Group.

The Coedana Granite.

Hornfels: Cryptocrystalline Hornfels. Crystalline Hornfels. Unity of the Hornfels. Composition. Origin of the Hornfels. Foliated Hornfels.

Diorites.

The serpentine suite: Serpentine. Pyroxenites. Gabbros. Dolerites. Mutual Relations. Associated Metamorphic Rocks (Talc-schist, Tremolite-schist, Ophicalcite, &c.). Deformation and Metamorphism. Marginal Rocks.

The Penmynydd Zone of Metamorphism: The Mica-schists. Quartz-schists. The Limestones. Graphite-schist. Rutiliferous-schists. The Hornblende-schists. The Glaucophane-schist. Its Origin. Banded Marginal Rocks. Origin of the Penmynydd Mica-schists. Conclusions.

The Gneisses: Hornblende-gneiss. Biotite-gneiss or Gneiss-proper. Its Granitoid Component. Its Foliated Component. Nature, Origin, and Relations of the Components of the Gneiss. Comparisons and Conclusions.

Foliation.

General mineral characters of the Mona Complex.

Chapter 5 — The palaeontology of the Mona Complex

Chapter 6 — The succession in the Mona Complex

Introductory.

Correlations within the complex.

Order of succession: Group Sequences and Junctions. The Bedded Succession. The Penmynydd Zone. The Gneisses. Local Successions.

Table of the general succession.

Chronological order of the succession: Ancient fragments. The Plutonic intrusions and the Penmynydd Zone.

Relation of the gneisses to the bedded succession.

The ancient floor.

Chapter 7 — The tectonics of the Mona Complex

Introductory.

The maximum primary recumbent structures: Evidence for Inversion. The Maximum Primary Folding as revealed in Holy Isle. The Maximum Primary Structures on the Main Island (with evidence for directions of close and gape). amplitudes, facies, and recapitulation.

The major, minor and minimum structures: The Major Secondary Folds and Thrusts. The Minor or Ternary Folding. Types of Minor Folding. Pitch. Minor Thrusting. Principles of Auto-clastic Mélange. The Minimum or Tessary Folding.

Structures of the second and third generations: The Valley Thrust-planes. The Foliation of the Western Region. Relations of the Penmynydd Metamorphism.

Later structures: Transverse Folds. Final Catamorphic Movements.

Folial relations: Relations to Bedding, Folding and Thrusting. Chronology of the Foliation.

Chapter 8 — General view of the Mona Complex

Introductory.

Developments in the several regions: Holy Isle. The Western Region. The Northern Inliers. The Northern Region. The Middle Region. The Gneissic Inliers. The Deri Inlier. The Pentraeth Ethers, The Aethwy Region.

Developments over the island considered as a whole: Probable thickness. Facies and physiography. Geographical distribution of the stratigraphical and tectonic members of the Complex. Arrangement of the Post-Recumbent Foldings. pitch, dip, and strike throughout the island. Distribution of the metamorphism. Laws of the Metamorphism.

Recapitulation.

Chapter 9 — The age of the Mona Complex

Relations of the Complex to Ordovician Rocks.

Relations of the Complex to Cambrian Rocks: The indirect evidence. Pebbles in conglomerates (with table). Horizons and localities of the conglomerates (with table). Pebbles from Llanberis and Bethesda. Pebbles from the Harlech Anticline. Review of the evidence. Conditions of the Cambrian erosion.

Conclusion.

[NOTE — See also pp.425–6, 559, 906]

Chapter 10 — The detail of the Mona Complex

Holy Isle.

Tracts West of the North Stack Fault. The North Stack and the Fault. The Stack Moor. The South Stack. The Stack Moor Syncline. Henborth and Llwyn-y-berth. Rhoscolyn.

The Country between the Two Main Faults: The Rhoscolyn Anticline. Rhoscolyn to the Tre-Arddur Gap. The Country about Holyhead. Holyhead Mountain.

District North-east of the Namarch Fault: Stanley Gate to Soldier's Point. The Breakwater Coast.

The Serpentine-Suite about the Strait of Holy Isle: Mainland and islets: Four-Mile-Bridge to Cymyran. The Lakes, Porth-delisc. The Strait Islets,

Holy Isle: Between the Strait and the Alluvium. West of the Alluvium. The Southern Margin.

The Western Region.

The New Harbour Group: The Sea-Board. The Interior.

The Gwna Group: Llanfaethlu to Brwynog. Llanrhyddlad. Foel High Land.

The Church Bay Tuffs.

Boundaries.

The Northern Inliers.

The Garn Inlier.

The Mynachdy Inlier.

The Fydlyn Inlier: Trwyn-y-crewyn to Fydlyn Beach. Fydlyn Beach to Porth-yr-hwch. Porth-yr-hwch.

The Gader Inlier.

The Corwas Inlier.

The Northern Region.

The Llanfairynghornwy Belt: Carmel Head to Gwaen-ydog. The Mynachdy Gneiss.

The Coeden Beds.

The Amlwch Beds: The Coast. The Interior.

The Gwna Beds of Gynfor, Pant-y-gaseg, and Wylfa: General Characters. Wylfa. Gynfor. Pant-y-gaseg.

The Skerries Group in the Trwyn Bychan Tract: Hell's Mouth to Porth Wen. Trwyn Bychan to Bull Bay.

The Skerries Grits between Llanfechell and Llan-rhwydrys.

The Three Mouse Islets.

The Skerries.

Basic intrusions of the North.

The Middle Region and its inliers.

Gneiss of the Middle Region: The Southern end. Allor. Llandry-garn and Gwyndy to Llechcynfarwydd. Henblâs to Mynydd-mwyn-mawr. Gneissic Inliers of the Middle Region. Basic Gneisses near Llangwyllog.

Gneiss of the Nebo Inlier: The Interior. The Coast.

The Coedana Granite.

Hornfels: The Coast, Llanfaelog, and the Marginal Aureole. The Xenoliths.

The Deri Inlier.

The Foel Inlier.

Mynydd Bodafon: The Quartzite, Hornfels; and Moor Flags. Tectonics.

The Penmynydd Zone of the Middle Region: The Coast. The Western Margin. The Rest of the Inland Tract. The Inliers.

The Gwna Beds and Tyfry Beds of the Eastern Middle Region: The Coast. South-eastern Margin. Between the Margin and the line through Cerrigceinwen. The Ceinwen Volcanic Zone. The Engan Spilites. The Western Tracts.

The Pentraeth Inliers.

The Western Inlier.

The Eastern Inlier: Dyffryn to Tyfry. Tyfry to the seaward end.

The Aethwy Region.

The Gwna Beds of the East: The Menai Coast. Cadnant to Red Hill. The Interior. The Eastern Margin. The Llanddona Highlands.

The Penmynydd Zone of the Aethwy Region: The Eastern and South-eastern Margins. The North-western Margin. The Centre. Mynydd Llwydiarth.

Gneiss of Holland Arms and Gaerwen (with Rhos-cefn-hir).

The Llanddwyn Wedge: Llangaffo to Newborough. The Dunes of Newborough. Llanddwyn Island. Carnarvon.

The Order of the minor sub-divisions of The Bedded Succession.

Order of the Sub-divisions of the Groups. Horizons of Development of the Penmynydd Metamorphism.

Chapter 11 — Recapitulation of the Mona Complex