Vol. 60.] METAMORPHISM IX THE LOCH-LOMOND DISTRICT. 19 



of strike, both the flexuring and the strata striking from north-east 

 to south-west. The rocks which emerge from below the great 

 syncline differ very greatly, as has already been stated, from the 

 same rocks to the south-eastward of the syncline. The area 

 south of Loch Katrine illustrates this admirably. In the rolling 

 and crumpled folds north-west of the trough grit-beds are fre- 

 quently noticed, but they can never be traced far ; the normal type i> 

 a glistening mica-schist, which apparently becomes more micaceous. 

 and certainly more fissile, to the north-westward, as gritty bands 

 become less and less frequent. The rocks invariably split along 

 the planes of foliation, and thus present micaceous surfaces giving 

 all the appearance of a phyllite ; but a careful examination shows 

 that to call them ' phyllites ' would misrepresent their composition. 

 If a good cross-fracture (a difficult thing to obtain) is examined, it 

 is seen that these schists are made up of folia or elongated phacoids 

 composed chiefly of quartz, separated by mere films of micaceous 

 minerals along which the rock naturally fractures. Thus the 

 quantity of the micas present is apt to be overestimated at first. 

 In the phacoids remains of allothigenic structures may often be 

 observed, long after all traces of a regular bed of grit have been lost. 

 A specimen (3681) from the shore of Loch Katrine, three-quarters 

 of a mile south -south-east of Stronachlachar Hotel, is a characteristic 

 example of this type of mica-schist. Xo grits have been recognized 

 in the locality. The specimen consists of alternating folia of granulitic 

 quartz and micaceous minerals, chlorite, white mica, and a little 

 biotite : the quartz has partly recrystallized, and contains the micas. 

 A few large allothigenic quartzes, however, are still present, but 

 they are almost entirely granulitized : and there are also several 

 much-fractured and decomposed remnants of plagioclase-pebbles. 

 Thus it is seen that, even in a locality where the rocks are typically 

 mica-schists, evidence of their having been grits may be obtained, 

 and that the grits were fairly coarse in grain may be deduced from 

 the size of the remnants of pebbles. 



Returning to the shore-section on Loch Lomond, we find at 

 Inveruglas a rock (8957 : PI. II, fig. 2) in which all allothigenic 

 minerals have disappeared, while distinct evidence of a new and 

 remarkable type of constructive metamorphism, to which allusion 

 has been made above, is obtained. The rock consists of quartz, 

 recrystallized, and often leached out into veinlets following the 

 foliation-planes, felspar in a few small decomposed fragments, and 

 well-developed micas, muscovite and a little biotite, which are both 

 included in the recrystallized quartz. Teins of calcite point to the 

 removal of lime from crushed and decomposed plagioclase. But 

 the most important point is the development of a few small clear 

 blebs of albite, which are chieflv associated with the micaceous folia. 

 The rock shows the first stage in the building-up of an albite- 

 gneiss. From this point onward it is impossible to note increase 

 in the dynamic metamorphism, as there are no clastic structures by 

 the destruction of which such metamorphism can be measured ; it 



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