388 J. CLIFTON WARD ON THE MICROSCOPIC STRUCTURE OF 



26. Notes on the Comparative Microscopic Bock-structure of 

 some Ancient and Modern Volcanic Rocks. By J. Clifton 

 "Ward, Esq., Assoc. R.S.M., F.Gr.S., of the Geological Survey 

 of England and Wales. (Read November 4, 1874.) 



[Plates XVII. & XVIII.] 



Contents. 

 Introduction. 



I. History of the Subject. 



II. Examples of Microscopic Rock-structure among Modern Lavas. 



1. Trachyte, Solfatara, near Naples (figs. 1 & 2). 



2. Leucitic Basalt, Torre dell' Annunziata, Naples (fig. 3). 



3. Leucitic Basalt, near Torre del Greco, Naples (figs. 4 & 5). 



4. Leucitic Basalt, Albano, near Rome. 

 Summary. 



III. Examples of Microscopic Rock-structure among the Lavas and Ashes of 



Wales. 



a. Aran and Arenig Felstones. 



1. Aran Mowddwy (figs. 16 & 17). 



2. Aran Benlynn (fig. 18). 



3. Y Foel-ddu. 



4. Efridd Trawscoed. 



b. Snowdon Felstones. 



5. Llanberis Route, Snowdon (fig. 19). 



6. Glaslyn, Snowdon. 



7. Llyn Cwlyd, Capel Curig. 



8. Llanberis Route, Snowdon (Slaggy Felstone, fig. 20). 



c. Ashes of Snowdon, Arenig, and the Arans. 



1. Glaslyn, Snowdon (fig. 21). 



2. The Arans (fig. 22). 



3. The Arenigs. 

 Summary. 



IV. Examples of Microscopic Rock-structure among the Lavas and Ashes of 



Cumberland. 

 Introduction. 



a. Cumberland Lavas. 



1. Eycott Hill (fig. 6). 



2. Brown Knotts, near Keswick (fig. 7). 



3. Latterbarrow,Wastwater (fig. 8). 

 General Remarks. 



b. Cumberland Ashes and Felstone-like Bocks. 



1. Typical Ash, Steel Fell, Wythburn (fig. 10). 



2. Altered Slate, Craig Wen, Capel Curig. 



3. Bleaberry Fell, near Keswick (fig. 9). 



4. Hart Side, North of Glencoindale Head (fig. 13). 



5. Base Brown, Borrowdale (figs. 11 & 12). 



6. Great Gable (fig. 14). 



7. Rigghause End, Vale of St. John (figs. 15 & 16). 

 c Manner of Metamorphism. 



d. Period of Metamorphism. 



e. Parallel Metamorphism of Welsh Lavas and Ashes. 

 /. Classification of Cumberland Lavas. 



g. Conclusion. 



