VOLCANIC ROCKS OF EAST LOTHIAN. 



125 



Certain parts of the sections are dusted over with a brown powdery material. A near 

 examination of these portions discloses in them the presence of small colourless patches 

 which, when rotated between crossed nicols, remain nearly or quite dark. These small 

 patches consist of nepheline, or of zeolitic products of its decomposition ; but only a close 

 examination of very thin sections enables one to detect the presence of occasional six- and 

 four-sided crystal-contours.* The mineral, however, has been very largely converted into 

 the zeolites, analcime, and natrolite, of which there is abundant evidence in the sections. 

 With regard to micro-chemical tests, a drop of hydrochloric acid placed upon a smooth 

 surface of the rock rapidly produces gelatinisation ; and the jelly, dried and treated with 

 acetate of uranium, develops abundant and characteristic crystals of uranate of sodium. 

 The distribution of the nepheline, and its zeolitic products of decomposition, is well 

 shown by treatment with hydrochloric acid, and subsequent staining with fuchsine. 



Mr Player has kindly analysed the rock for me, and his results are the following : — 



Analysis of Phonolite (Sect. No. 4526). 



Silica, 











56-8 



Titanic acid, 











•5 



Alumina, 











19-7 



Ferric oxide, 











2-2 



Ferrous oxide, . 











35 



Manganous oxide, 











•2 



Lime, . 











2-2 



Magnesia, 











•4 



Soda, . 











43 



Potash, 











7-1 



Loss by ignition, 











2-5 





99-4 





Sp. G 



= 2-588 









The small amount of magnesia ("4 per cent.), and the high percentage of alkalies (1T4 

 per cent), are interesting points brought out by this analysis. 



Summary. 



The Carboniferous volcanic rocks of East Lothian (the Garlton Hills, &c.) consist of 



(1) A lower, basic series, comprising felspar-free basalts, rich in olivine and augite, 

 and containing much glassy matter with occasional crystals of nepheline (limburgite of 

 Whitelaw Hill) ; normal olivine-basalts (e.g., Kippie Law and Hailes Castle) ; and a very 

 felspathic type (labradorite-basalt of Markle Quarry). 



(2) An upper, trachytic series, which builds the main portion of the Garlton Hills, 

 comprising trachytes with porphyritic sanidine (e.g., Peppercraig, Kae Heughs, and 



* The low index of refraction, and the absence of a needle-form, serve as a distinction from apatite. Professor 

 Rosenbusch of Heidelberg, to whom I submitted specimens, confirms the identification of the nepheline, and refers the 

 rock to the trachytic phonolites of his classification. 



