498 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Fig. 6. A portion of a crystal of chloride of potassium formed at 100° C. X 150. 



Fig. 7. A iluid-cavity in chloride of sodium formed at 100° C. X400. 



Figs. 8, 9, 10. Fluid-cavities in chloride of potassium formed at 100° C. 

 8, X300; 9, X400; 10, X200. 



Figs. 11, 12, 13. Fluid-cavities in chloride of sodium formed at 100° C, in a 

 strong solution of bichromate of potash. 11,13, X1000; 12, X600. 



Figs. 14, 15, 16. Crystals of bichromate of potash and attached fluid-cavities, in 

 chloride of sodium formed at 100° C, in a concentrated solution of the 

 bichromate. 14,15, X100; 16, X70. 



Fig. 17. A fluid-cavity in chloride of sodium formed at 100° C, in a concen- 

 trated solution of bichromate of potash. X 800. 



Figs. 18, 19. Fluid-cavities in chloride of sodium formed at 100° C, in a strong 

 solution of chloride of potassium. 18, X800; 19, X1200. 



Fig. 20. A fluid-cavity in chloride of sodium formed at 100° C, in a strong 

 solution of hydrochloride of ammonia. X 800. 



Figs. 21, 22. Fluid- cavities in nitrate of potash formed at the ordinary tempe- 

 rature. 21, X400; 22, X200. 



Fig. 23. A fluid-cavity in binoxalate of ammonia formed at the ordinary tem- 

 perature. Xl50. 



Figs. 24, 25. Fluid- cavities in sulphate of zinc formed at the ordinary tempe- 

 rature. X130. 



Plate XYII. 



Fig. 26. A portion of a crystal of alum formed at 50° C. X 100. 



Figs. 27, 28. Fluid-cavities in alum formed at 50° C. 27, X100 ; 28, X400. 



Fig. 29. A gas-cavity in a portion of a crystal of alum formed at 50° O. X 50. 



Figs. 30, 31. Fluid- cavities in alum that have lost water by drying. 30, X800 ; 

 31, X400. 



Fig. 32. A portion of a crystal of bichromate of potash, with bands of fluid- 

 cavities. X 200. 



Fig. 33. A fluid-cavity in bisulphate of potash, which totally reflects the trans- 

 mitted light. X200. 



Figs. 34, 36, 37. Fluid-cavities in chloride of sodium formed above the level of 

 the liquid at 100° C. 34, X800; 36,37, X1000. 



Fig. 35. A gas-cavity in chloride of sodium formed above the level of the liquid 

 at 100° C. X600. 



§ 2. Formed by Sublimation. 



Fig. 38. A gas-cavity in hydrochlorate of ammonia. X 600. 

 Fig. 39. A gas-cavity in corrosive sublimate. X400. 



§ 3. Formed from a state of Igneous Fusion. 



Fig. 40. A portion of a crystal of basic silicate of protoxide of iron, from a cop- 

 per slag. X 200. 



Figs. 41, 42, 43. Grlass-cavities in a portion of a crystal of basic silicate of prot- 

 oxide of iron, from a copper slag. 41, X1600 ; 42, X400; 43, X600. 



Figs. 44, 45. Part glass-, part stone-cavities in a portion of a crystal of basic 

 silicate of protoxide of iron, from a copper slag. 44, X 1200 ; 

 45, X1600. 



Fig. 46. A stone-cavity in a portion of a crystal of basic silicate of protoxide of 

 iron, from a copper slag, X 1600. 



Fig. 47. A stone-cavity in pyroxene, from a blast-furnace slag. X 800. 



Fig. 48. A glass-cavity in Humboldtilite, from a blast-furnace slag. X400. 



FLriD-Ci T iTiES in Natttkal Mineeals. 



Figs. 49, 50, 51. In quartz of a vein at Mousehole, near Penzance. X800. 

 Fig. 52. A fluid-cavity containing two fluids, in the quartz of a porphyry at 

 Cove, near Aberdeen. X 2000. 



