PROCESS-BLOCKS AND OTHER ILLUSTRATIVE FIGURES. XIX 



Fig. Page 



1 . Section from Penbryn Dingle to Trefnant Dingle 420 



2. Section exposed in Gwern-y-brain 422 



3. Section near the top of Gwern-y-brain Valley 428 



4. Section reproduced from Murchison's ' Silurian System ' 



1839, p. 304 431 



5. Map illustrating the exposures in Cwm Caethro 437 



6. Map showing the Wenlock zones exposed in Guilsfield Brook . 438 



7. Generalized section from east to west, illustrating the structure 



of [part of North-eastern Montgomeryshire] 443 



8. [Microscope-section.] Bostonite of the Welshpool Dyke 447 



9. Jonesella crepidiformis, J. obscura, and Melanella hemidiscus, 



gen. et sp. nov 452 



10. Arnplexograptus perexcavatus, Lapw 456 



11. Young form of Monograptus vulgaris 456 



1. Map of the neighbourhood of the Great House, Golden Hill 



(Monmouthshire) 461 



2. Fine-grained Old Red Sandstone at the contact with the 



monchiquite 463 



3. [Microscope-section showing various parts of the monchiquite- 



dyke] 467 



1. Topographical map of Gower and related areas 478 



2. Geological map of Gower 479 



3. D 2 _ 3 limestones and shales in the ' Black Lias ' Quarry at 



Oystermouth 492 



4. Comparative vertical sections through the Avonian of Gower . 506 



5. Diagram showing the relation of the dolomite in a partly- 



dolomitized pseudobreccia, to unrecrystallized calcite 510 



6. Ideal section across a lagoon-area at right angles to the coast . 512 



7. Diagram showing the probable relations between the uncon- 



formities at West Williamston and Pendine 527 



8. Diagram showing the variation in depth of the Avonian Sea at 



successive times, deduced from the sequence in Gower 533 



9 & 10. Zaphrentis oystermoutkensis, sp. nov 554, 555 



