FROM THE TERTIARY LAVAS AROUND BEN MORE, MULL. 9 



calcite to be of frequent occurrence in the amygdales, but, as a matter of fact, it is 

 rare and has been noted on few specimens. On one of these it occurs in a fairly large 

 hollow in scolecite as a white, crystalline, much-cleaved mass, studded with yellow 

 garnets. It lies near the walls of the vesicle and is separated from the scolecite 

 by a space partially filled with yellow epidote. The surface of the scolecite adjoining 

 this space is flat and shows the characters possessed by the walls of the rectilinear 

 cracks already described as occurring in this mineral. Support is thus lent to the 

 view that these cracks were once occupied by calcite, which has since been removed. 



Chabazite and Thomsonite. — In addition to scolecite these are the only other 

 zeolites which have been noted on An Gearna, and they are extremely rare. The former 

 mineral has been found on only one specimen, where it occurs as simple rhombohedra 

 lining a cavity in white, massive prehnite spotted with reddish-brown garnet ; albite 

 and epidote are also present. Thomsonite has been noted in sheaf-like growths 

 intimately associated with prehnite, albite, and scolecite. It has also been found 

 on the north-east slope of Beinn Fhada associated with albite and prehnite, and with 

 like associates on Coire Bheinn. 



Hornblende can be observed occasionally in hand-specimen as tufts or aggregates 

 of acicular crystals always near the walls of the vesicle. It spears the scolecite and 

 is intimately associated with epidote. As will be shown later, it is a common 

 microscopic mineral in the amygdales. 



The Minerals of Maol nan Damh. 



To appreciate correctly the significance of the most unusual mineral association 

 described above, it .is necessary to study the occurrences on the neighbouring hills. 

 In the paper already quoted, Mr Currie records the presence of scolecite, epidote, 

 calcite, celadonite, heulandite, and, much more rarely, stilbite, and prehnite from the 

 upper lavas of the south-western side of Maol nan Damh, a spur of Ben More running 

 in a south-westerly direction towards Loch Scridain (see fig. 1). He very kindly 

 presented specimens to the Royal Scottish Museum, and from an examination of 

 them I came to the conclusion that what had been determined as heulandite was 

 in reality albite. In the course of correspondence with me Mr Currie very frankly 

 stated that he, too, was now of the same opinion, and from an examination of 

 specimens collected by Mr E. M. x4nderson and myself there can be no doubt that 

 albite is of very frequent occurrence in the vesicular lavas at this locality. 



The zeolite-filled cavities are if anything larger and more abundant than those 

 of An Gearna, and it is clear that here we are dealing with a similar set of rocks. 

 Scolecite, as described by Mr Currie, is by far the most abundant mineral, and 

 associated with it are epidote, chlorite, albite, calcite, and, more rarely, prehnite. 

 Heulandite and stilbite are exceedingly rare and have been noted on only one 

 specimen, where they fill up the spaces between a crystalline aggregate of quartz, 

 albite, and epidote, whilst chabazite has been noted in a vesicle filled with an 



TRANS. ROY. SOC. EDIN., VOL. LI, PART I (NO. 1). 2 



