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



selves at the north-western extremity of the ridge at heights of 1200-1500 feet. 

 There the vesicles are filled with scolecite underlain by a layer of pale green or 

 yellow epidote intimately associated with garnet, prehnite, and, frequently, albite. 

 The boundary of this layer with the zeolite is highly irregular, and every now and 

 then it sends oft" growths into the scolecite, tufted aggregates of which can often 

 be seen enclosed in the prehnite and epidote. On some of the specimens there is 

 a white massive mineral which occasionally merges into opaque, white tufts of 

 zeolite. When examined under the microscope the massive mineral proves to be 

 prehnite, which is clearly replacing the scolecite originally in the vesicle. Beautiful 

 specimens also occur in which the scolecite is sprinkled with groups of crystals of 

 epidote and garnet, pale pink, yellow, or even red in colour. 



A peculiar vesicular, pale gray lava has also been noted in which the vesicles 

 present rather unusual features. They are lined with a thin layer of black chlorite, 

 which is succeeded by epidote or stilbite, sometimes well crystallised, or by a massive 

 aggregate of the two in which the epidote occurs as grains and crystals enclosed in 

 the zeolite. When the stilbite is absent the epidote is abundant, and vice versa. 

 Some of the vesicles, again, are lined with dull brown botryoidal material which, 

 on examination, proves to be epidote coated with prehnite. A study of the vesicles 

 in this rock strongly suggests that some of the epidote at least has been developed 

 at the expense of the lime-bearing zeolite. 



Thomsonite is occasionally found on this part of the hill. It is underlain by the 

 usual zone of epidote and prehnite, spotted and veined, however, with albite. 



Along the north-east slope of the hill the zeolites and, indeed, amygdales get 

 much rarer as the junction of the granophyre with the lavas is approached, and, 

 when found, they show unmistakable signs of having been baked and altered. At 

 a point almost S.S. W. of the summit of Beinn a' Ghraig prehnite is of common 

 occurrence in the vesicles and, occasionally, white fibrous masses are found which 

 look like scolecite, but, on examination, prove to be prehnite, which is replacing it. 

 On one or two specimens cleaved masses of white calcite occupy hollows in massive 

 white prehnite, and at the junction of the two minerals there are exceedingly minute 

 crystals of white, perfectly colourless garnet. 



Still nearer the granophyre the original character of the amygdales is completely 

 changed ; the j miction with the walls loses its sharpness, and the material filling the 

 cavities seems to merge into the surrounding rock. Prehnite veined and riddled 

 with a pale yellow epidote and garnet, pale yellow to almost black in colour, is very 

 common, whilst in other cases the vesicle is filled with a pale pink massive material 

 which consists largely of a mixture of garnet and epidote. 



■It is thus clear from the field evidence that, the zeolites were formed before the 

 intrusion of the granophyre and have been metamorphosed by it. Microscopic exami- 

 nation of a scries of sections through the amygdales confirms this conclusion and 

 n veals a number of interesting contact materials not visible in hand-specimen. But, 



