4 MR W. F. P. M'LINTOCK ON THE ZEOLITES AND ASSOCIATED MINERALS 



Beina Fhada and cuts another series of thin basaltic sheets with a general westerly 

 dip which arc distributed throughout the district. Still earlier sheet-like masses 

 of coarse dolerite form small scattered patches, of which some at least are later than 

 the early granophyre. 



" Some north-westerly dykes are earlier than the Beinn a' Ghraig granophyre, but 

 the greater number of dykes belong no doubt to the north-west series proper and 

 are the latest intrusions." 



" The shoulder of Ben More known as Maol nan Damh is composed in the main of 

 flat or very gently inclined lavas. Those forming the lower slopes of the hill are 

 more basic, but the difference in character is not very marked and they are rather 

 difficult to separate from the overlying flows, although the former are mapped as 

 basalts and the latter as andesites.* The screes which flank the western slopes are in 

 the lower more basic lavas. 



" The largest intrusive mass is a flat sill of mugearite some 200 or 300 feet in 

 thickness. This comes some 500 feet above the screes referred to. There are also a 

 large number of minor intrusions, including porphyritic and non-porphyritic dolerite, 

 and one or two that are more acid in character. As a whole, however, they are not 

 so numerous as those which intersect the lavas in the higher portion of Ben More." 



The Minerals of An Gearna. 



One of the most convenient places for studying the mineralogy of the lavas is the 

 ridge of An Gearna referred to above. On the north-eastern slope at a height of 

 about 1200 feet, large amygdales, filled chiefly with a white fibrous zeolite, make their 

 appearance in the screes and become plentiful at heights of 1300-1500 feet. The 

 size of these amygdales is phenomenal, measuring, as they do, as much as 15 cm. x 

 10 cm. It is noteworthy that the lavas of the upper part of the hill alone yield the 

 zeolite-filled vesicles ; the amygdales in the lower lavas are small and are filled mostly 

 with compact, massive albite. The fibrous zeolite is scolecite, and associated with it 

 are epidote, prehnite, garnet, albite, and, much more rarely, hornblende, calcite, 

 chabazite, and thomsonite. 



Scolecite has usually been considered one of the rarer Scottish zeolites, f but on 

 An Gearna it occurs in profusion, whilst it is also common on Beinn Fhada and Maol 

 nan Damh ; on Coire Bheinn, a hill lying two miles south-west of An Gearna, it is 

 much rarer, although good specimens have also been got from there. It occurs in 

 white fibrous aggregates and crystals, which in some cases reach a length of 10 cm., 

 but, although many cavities have been broken open, no terminated crystal has been 

 observed. In some cases when an amygdalc is broken across, the scolecite shows a 

 series of perfectly sharp rectilinear cracks or veins with perfectly flat, lustrous 



* Microscopic examination has since shown that the lavas provisionally mapped as andesites are olivine basalts 

 much like the underlying flows. 



t Of. J. G. Goodchild, " Natural History of Scottish Zeolites," Trans. Glas. Geol. Soc, 1903, vol. xii, suppt , p. 62. 



