698 SEC. 16. GEOLOGY AND MINING. 



B. Illustrating the Metamorphism of Volcanic Rocks around the Granites of 

 Eskdale and Shap. 



1. Altered ash, Yewbarrow, x 50. 



2. Altered contemporaneous trap (?) close to granite, x 50. 



3. Same field of view, in polarized light, x 50. 



4. Highly altered ash, close to granite. (Polarized light), x 50. 



5. Bastard granite. (Polarized light), x 50. 



6. True granite, x 50. 



7. Junction of highly altered ash with Shap granite. (Polarized light 



x25. 



C. 



1. Altered Skiddaw slate passing into quartz felsite, Clough Head, St. 



John's Vale, x 30. 



2. Quartz felsite, St. John's Vale, x 30. 



3. Altered Skiddaw slate, Eed Pike, x 70. 



4. Buttermere, x 70. 



5. Syenitic granite, Scale Force, Buttermere, x 30. 



6. Spherulitic felsite, Carrock Fell summit. (Polarized light), x 10. 



7. Hypersthenite, WTiite Crags, Carrock. (Polarized light), x 10. 

 1. Fine-grained band in hypersthenite. (Polarized light),"x 10. 



3253g. Plates illustrative of Structures in Felspars, 

 Leucite, Obsidian, and Perlite, from drawings made partly in 

 pencil, partly in lamp-black, by Frank Rutley, F.G.S., H.M. 

 Geological Survey. Plates I. and II. illustrate a paper in the 

 Quart. Journ. of the Geological Society of London for Aug. 1875. 

 Plates III. and IV. illustrate a paper in the Royal Microscopical 

 Society's Transactions, March 1876. 



Frank Rutley ', Geological Survey Office. 



PLATE I. 



Fig. 1. Orthoclase, Arendal, showing crystals arranged in two directions, 

 other than those of striation. x 50 (polarized light). 



2. Felspar crystal in perlite, Schemm'tz, Hungary, showing partial 



cross-hatching, x 55 (polar.). 



3. Crystal in trachyte, Berkum, near Bonn, Khine, showing internal 



curved divisional markings, with lines crossing at right angles in 

 the lateral areas, x 115 (polar.). 



4. Partially formed, or partially disintegrated crystal in obsidian, 



Mexico, x 175 (dark-ground illumination). 



5. Patches of cross-hatched felspar in oligoclase, Twedestrand, Norway. 



x 115 (polar.). 



6. One of the above patches, showing partial cross-hatching, x 350 



(polar.). 



PLATE II. 



Fig. 1. Minute crystal in obsidian, Mexico, x 240. 



2. Diagrammatic exaggeration of the above. 



3. Crystal from trachyte, Berkum, Rhine, x 90 (polar.). 



4. Crystal from basalt, Cleveland, showing rectangular banding and 



subordinate oblique striation, the latter possibly indicating planes 

 connected with twinning on the Baveno type, x 45 (polar.). 



5. Crystal in obsidian, Mexico, x over 100. 



