I. GKOLOGY. 845 



10. Parallel roads of Glen Roy. 



11. View of Exmouth. 



12. Brent Tor near Tavistock. 



13. Dunolly Castle near Oban. 



14. View of Shapton Sands. 



15. View of south coast of Lyme Regis with Portland in the 

 distance. 



3292. Geology. Collection of specimens of felspars and 

 amphibolitic rocks from Belgium and the French Ardennes. This 

 collection comprises about 20 specimens, average dimensions 10 

 centimetres by 15. 



Six chromolithographs of drawings of minerals and rocks as 

 seen through the microscope. A. Renard, Louvain. 



3293. Specimens illustrating the production by Compression 

 of Natural and Artificial Slaty Cleavage. H. C. Sorby. 



Specimens of slate rocks, showing, by various facts, that they have been 

 greatly compressed in a line perpendicular to the cleavage. 



Pipe-clay mixed with portions of blue paper, and also with iron scales, 

 being the results of the first experiments made to show that a structure like 

 that which causes the cleavage in slates can be artificially produced by 

 pressure. 



Artificial cleavage in compressed flaky graphite, being as perfect as that 

 in any slate rock. 



3294. Specimens illustrating the Metamorphic Origin of 

 Mica Schist, and the difference between stratification-foliation 

 and cleavage-foliation. H. C. Sorby. 



" Ripple drift " in slate rocks in which the cleavage cuts the stratification at 

 a considerable angle. 



" Ripple drift" in contorted and highly metamorphosed mica schist, thus 

 proving the original stratified nature of the rock. 



Mica schist with foliation in the plane of stratification, being rock metamor- 

 phosed before being compressed. 



Mica schist with foliation in the plane of cleavage, developed by compres- 

 sion, before the work was metamorphosed. 



3295. Microscopical Photographs of sections of iron and 

 steel. H. C. Sorby. 



The above were photographed by means of strong surface illumination, 

 and show structures due to the arrangement of crystals of iron combined with 

 a varying amount of carbon, of portions of slag, and of crystalline plates of 

 graphite. Note the contrast betAveen the structure of cast iron, cast steel, 

 and meteoric iron, although all have solidified from fusion. 



3296. Microscopical Sections of iron and steel. 



H. C. Sorby. 



The above were prepared by very carefully grinding down and polishing the 

 surface so as to avoid all such burnishing action as would alter the form or 

 structure of the ultimate crystalline particles. The whole section is then 

 placed in very dilute nitric acid, and carefully examined in water under the 



