60 J. S. G. Wilson Sf H. B. Muff— The Hill of Beat h. 



continuous with the base of the rock. There is no felspar. The rock 

 has some affinities with the biotite-bearing limburgite of Carboniferous 

 age from Whitelaw Hill, East Lothian, described by Dr. F. H. Hatch/ 

 but it resembles more closely certain monchiquites of the same age 

 from East Lothian to be described by Mr. E. B. Bailey in the forth- 

 coming memoir on that district, and probably it is best termed an 

 augite-monchiquite. Though evidently very basic in composition, it is 

 too decomposed for the determination of the specific gravity to have 

 any value, and further it contains numerous small, irregular vesicles 

 filled with zeolites or calcite. There are also small but less well- 

 defined spots free from magnetite. They are occupied by minute 

 prisms of pale green augite embedded in analcime or calcite. Often 

 the augite prisms form a distinct border on the periphery of the spot, 

 the centre of which is occupied by calcite or analcime or both these 

 minerals, whilst the biotite scales are sometimes very abundant in 

 a narrow rim immediately outside the augite border. Though some- 

 what resembling the reaction-rims of augite, which surround xenocrysts 

 of quartz in some basic rocks, these spots cannot be explained in that 

 manner. Neither is there any sign of the regular crystallization of 

 the augite in spherulitic fashion from a centre, or from points on the 

 wall of the cavity. It is difficult to discriminate between two possible 

 explanations. The spots might be due to an attempt on the part 

 of the analcime to form definite crystals, which have succeeded in 

 pushing away the magnetite and biotite, but the augite has only been 

 collected on the borders. It is possible, however, that they are early- 

 formed steam cavities, into which still unconsolidated parts of the 

 magma have soaked and there crystallized out. There would be 

 nothing surprising in the early formation of steam cavities in a rock 

 containing a considerable quantity of analcime. 



The age of the neck cannot be determined with absolute certainty. 

 It must be younger than the rocks which it pierces, viz. the lower 

 part of the Coal-measures of the Carboniferous Limestone series, but 

 the higher limit of its age is indefinite. There are no bedded volcanic 

 rocks in the neighbourhood with which it can be connected, but in the 

 Saline Hills some 6 miles away in a west-north-westerly direction, 

 similar tuff-necks are associated with bedded tuffs lying on the position 

 of the Upper Limestones above the coal-bearing group, and Sir 

 Archibald (ieikie has classed the Hill of Beath neck with this group 

 of Carboniferous puys.- The petrological evidence given above is in 

 conformity with this correlation, for the monchiquite clearly belongs 

 to the Carboniferous and not to the Tertiary igneous magma. 



Amongst the many volcanic necks, between two and three hundred 

 in number, which pierce the Old Red Sandstone and Carboniferous 

 formations in the south of Scotland, several have had their subterranean 

 extension proved by mining operations. Perhaps the best known cases 

 are those in the Ayrshire Coalfield.^ An instance in which a mine 

 was driven from side to side of a neck, situated about 2 miles south- 

 west of Muirkirk in Lanarkshire, is given in the "Explanation of 



1 Trans. Roy. Soc. Edin., 1892, vol. xxxvii, p. 116. • Loc. cit. 



3 Memoirs of Geol. Surv. Scotland, Explanation of Sheet 22, p. 25, and 

 Explanation of Sheet 14, p. 22. 



