VOLCANIC ROCKS OF EAST LOTHIAN. 



117 



occasionally seen, being conspicuous by reason of their great length ; and, here and there, 

 scales of brown mica are present. In places the colourless " base " shows weak double 

 refraction, and a close examination now and then discloses the presence of a six- or four- 

 sided crystal of a colourless and pellucid mineral. The low index of refraction, shown by 

 its faint outline and clear aspect, distinguishes it from apatite. Probably it is nepheline. 

 The rock gelatinises readily with cold hydrochloric acid, and the jelly contains much 

 soda, as shown by treatment with uranium acetate. Mr Player has been good enough 

 to analyse a specimen of this rock, with the following result : — 



Silica, . 











40-2 



Titanic oxide, 











2-9 



Alumina, 











12-8 



Ferric oxide, 











4-0 



Ferrous oxide, 











10-4 



Lime, . 











10-4 



Magnesia, 











11-9 



Potash, . 











•8 



Soda, . 











27 



Loss by ignition 











3-4 



99-5 



Phosphoric acid is present. Sp. G. = 3 "03. 



The points brought out by this analysis are the low percentages of silica (40 per cent.), 

 and alkalies (3*5 per cent., mostly soda), the high percentage of ferrous oxide (10'4 per 

 cent.), magnesia (11 "9 per cent.), and lime (10 "4 per cent.), and the comparatively large 

 amount of titanic acid (2*9 per cent.). The titanic acid appears to be mainly present in 

 the augite, as the iron-ore, when isolated, proved to be magnetite and not ilmenite. 

 Knop found 4 - 5 7 per cent, of titanic acid in the augite of the limburgite of the 

 Kaiserstuhl in Breisgau. # 



The Olivine-Basalt of Kippie LawA — This is a dark compact rock, in which small 

 glistening facets of felspar can be seen without the aid of a lens. The examination of a 

 thin section under the microscope reveals the presence of porphyritic crystals of felspar 

 and olivine, lying in a ground-mass composed of lath-shaped felspars, granular olivine 

 and magnetite, and microlitic augite.| Olivine was originally the most abundant con- 

 stituent, but that mineral has, during the processes of chemical change that make up the 

 life-history of a rock, been converted into a fibrous aggregate of serpentine. With the 

 serpentine limonite is associated, this mineral having been deposited along the boundary 

 edges and in the cleavage cracks. 



The felspar is not abundant as a porphyritic constituent. It is a colourless and fresh 



* A. Knop, Zeitschrift fur Krystallographie, vol. x., 1885, p. 58. 



t No. 631 of the Survey Collection. 



I The Kippie Law type is occasionally found in other areas occupied by the Carboniferous volcanic rocks of 

 Scotland. Thus it occurs south of Jedburgh, at Neides Law and Bonchester Hill, also in the Campsie Hills, 1| miles 

 north of Lennoxtown. It is nearly allied to rocks of the Dalmeny type, which are abundantly distributed. It differs 

 from these in the presence of porphyritic felspars. 



