FROM THE TERTIARY L^VAS AROUND BEN MORE, MULL. 19 



is clear and transparent and contains crystals of epidote, showing distinct signs of 

 corrosioD, and also fibres and crystals of pale green slightly pleochroic augite [109]. 

 These veins resemble in some respects the contemporaneous veins described by 

 .Dr J. S. Flett * as occurring in the teschenite of the Barnton railway cutting, 

 Midlothian. 



A few exceptional vesicles have also been noted. Mention has already been made 

 of one lined with albite pseudomorphous after analcite. Under the microscope the 

 pegmatitic layer of augite, albite, magnetite, and chlorite is seen to be well developed 

 and is succeeded by the albite-pseudomorphs. A smaller vesicle underlies the main 

 one and is filled with albite secondary after analeite, chlorite moulded upon the 

 pseudomorphs and purple augite which occurs in large crystals lying around the walls 

 or stretching across the vesicle and projecting into the larger amygdale through a 

 canal which connects the two. The mode of occurrence of albite in this amygdale 

 points to an increase in temperature which may have been caused by local circum- 

 stances during the period of vesicle-infilling or by the injection of some intrusion 

 long after the zeolite was formed. The absence of any other sign of metamorphism 

 in the rock points to the former explanation being the probable one. 



Another specimen shows a fairly large vesicle filled with chlorite throughout 

 which are scattered a number of white spots. In thin section the rock is a typical 

 basalt showing the usual features, but the first mineral to be deposited in the 

 amygdale was garnet. It occurs as a pale brown layer of variable thickness and 

 exhibits signs of corrosion on its inner margin where it is overlain by scolecite or 

 chlorite. In places signs of an hexagonal outline are visible in some of the grains 

 lying away from the layer, but they are always corroded and tend to be circular. 

 The further the grains are removed from the walls the more do they show signs of 

 replacement, and in one or two instances they are represented by spots which are 

 doubly refracting and which merge into the surrounding zeolite. The garnet is 

 associated with yellow epidote, which seems to replace it in parts, and also with what 

 is apparently diopside. The latter mineral occurs as prisms showing good cleavage, 

 high refraction and birefringence, and an extinction angle of about 33° ; the mineral 

 is positive. The scolecite occurs in the usual fibrous forms. It is sometimes quite 

 clear, especially when it is adjacent to the garnet, but more often it is turbid ; it 

 contains corroded grains of garnet, fibres of diopside, which also show signs of replace- 

 ment, and epidote. Patches of heulandite are also present in the scolecite ; they 

 contain grains of garnet and epidote and their junctions with the scolecite are highly 

 irregular [78]. 



Grains of garnet have also been observed in a few other slides. In one of these 

 [23] it occurs as minute crystals, six-sided in section, enclosed in clear scolecite or in 

 chlorite ; in another slide there is a fairly well-defined band of greatly corroded grains 

 lying between the rock and the overlying chlorite-scolecite zone [68] ; whilst in a 



* Mem, Gcol. Surv., " The Neighbourhood of Edinburgh," 1010, p. 208. 



