Vol, 60.] METAMOEPHIS3I IN THE LOCH-LOMOND DISTRICT. 21 



but the albites coDtain numerous inclusions, chiefly of magnetite, 

 which are sometimes so abundant as to show the direction of 

 original foliation or bedding, as in the last specimen. The 

 micaceous minerals, however, are never included in the albites. 



The next specimen, from Creag an Ardain (8988), shows a 

 still further advance : the albites are larger and more conspicuous, 

 and are aggregated more distinctly into folia or lenticles, while the 

 quartz is also to a great extent segregated out into lenticles. The 

 albites are associated with a large quantity of chlorite and some 

 white mica, while biotite is no longer present. 



In the next slide (8989), from Ardvoirlich, the albites are even 

 more conspicuous, and the rock may be described as a typical 

 albite-gneiss. The association of the albite with chlorite is again 

 to be noted, and the inclusion of quartz, magnetite, and epidote in 

 the albites. The epidote is important, its occurrence pointing to the 

 presence of lime, derived probably from destroyed plagioclase. 



Eudha Ban. from which the next specimen (8990, PI. IV, figs. 1 

 & 2) is taken, has long been a famous locality for albite-gneisses. 

 All the rocks in this neighbourhood contain a large percentage of 

 albite, and when the grains of this mineral are large they weather- 

 out like the pebbles in a grit, giving almost a clastic appearance to 

 highly-crystalline rocks. The slide shows very clearly the segre- 

 gation of the materials into folia, quartzose lenticles alternating 

 with those rich in albite. The quartzose lenticles often attain a 

 large size, and appear as discontinuous veinlets in the matrix ; but 

 it is quite evident that these veinlets belong essentially to the rocks 

 in which they occur, and the silica has not been introduced from 

 elsewhere. 



Another slide from farther north, at Stuckindroin(8991), present:? 

 the same characteristics in a rock of more siliceous composition : 

 albite and chlorite, though present in considerable quantity, being 

 less conspicuous than quartz and muscovite. A few small garnets 

 are occasionally present in these rocks, but they are comparatively 

 rare, and never attain a sufficient size to be conspicuous in hand- 

 specimens. Calcite-veins are often fairly numerous, biotite i:? 

 almost, if not entirely, absent, while chlorite is abundant. 



On the whole, the rocks in this belt of country, from Inveruglas 

 to Stuckindroin, are remarkably constant in character: they are 

 all albite-gneisses produced by a constructive meta- 

 morphism, which reaches its maximum about the neighbour- 

 hood of Ardvoirlich and Eudha Ban, and does not appear to 

 decrease to the northward. Two points are worthy of attention : 

 (1) that the albites show a tendency to include all the other 

 minerals, with the exception of micas and chlorite •. and (2) that 

 the albites give no indications of having been affected by movement 

 of any kind — in fact, the lines of inclusions not infrequently show 

 the minute puckering and folding which was the latest movement 

 to affect the rocks : thus proving that the albites have developed 

 since the movement ceased. 



