228 REV. J. MILNE CURRAN. 



no apparatus at my command will show interference figures in so 

 small a crystal. Mr. Smeeth suggests that it may be microsomite. 

 Mica can also be recognised in the ground mass of most slices. 

 It occurs in small blades and irregular plates. The blades are 

 strongly dichroic. They can be detected by rapidly rotating the 

 lower nicol of the microscope. 



Scattered through the micro-crystalline base perfectly clear and 

 isotropic patches are noted. These are absolutely isotropic. Fine 

 needle-like bodies shoot through this clear mass, but without 

 affecting its isotropic character. This is a soda bearing, and is 

 most probably sodalite. It might be described as a glass and a 

 portion of the base, but on a careful examination it will be seen 

 as a mineral clearly separate from the base, and in no instance 

 merging into it. It is soluble in cold hydrochloric acid. The 

 acid acts on it without effervescence. If a portion of a cover 

 glass is removed and a second cover glass arranged so as to form 

 a cell that may be filled with acid, the action can be noted under 

 the microscope. A few bubbles of gas are given off from parts of 

 the slide but not from the soda mineral. This latter disappears 

 gradually, sometimes canals are developed as it goes into solution 

 but giving no clue to any crystalline structure. After treatment 

 with acid the whole surface has a muddy and dull appearance ; 

 even in polished slabs this action of cold hydrochloric acid is 

 remarkable. The acid always shows cubes of sodium chloride on 

 evaporating to a syrupy consistency. The easiest method of view- 

 ing the abundance of sodium chloride crystals formed by acting 

 on this rock with hydrochloric acid is as follows : Grind one 

 gram of the basalt in an agate mortar, just moisten with water 

 and then cover with strong hydrochloric acid ; after standing 

 overnight (without warming) the acid will have gelatinized ; add 

 some weak acid, filter and evaporate to the volume of say two or 

 three drachms; then further evaporate on a watch glass, at lowest 

 temperature practicable, when the cubical crystals will appear, and 

 if the evaporation is conducted slowly enough, of a size visible 

 without a lens. (See Plate n.) 



