. The Quarterly journal of the Geological Society of London. s rock shows the first stage in the building-up of an albite-gneiss. From this point onward it is impossible to note increasein the dynamic metamorphism, as there are no clastic structures bythe destruction of which such metamorphism can be measured ; it c2 20 MR. E. H. CUNNINGHAM-CRAIG ON [Feb. 1904, is evident, however, that in the area north-west of Inveruglas thedynamic metamorphism does not diminish, and it may have constructive metamorphism increases rapidly. Three specimens from the eastern side of the
. The Quarterly journal of the Geological Society of London. s rock shows the first stage in the building-up of an albite-gneiss. From this point onward it is impossible to note increasein the dynamic metamorphism, as there are no clastic structures bythe destruction of which such metamorphism can be measured ; it c2 20 MR. E. H. CUNNINGHAM-CRAIG ON [Feb. 1904, is evident, however, that in the area north-west of Inveruglas thedynamic metamorphism does not diminish, and it may have constructive metamorphism increases rapidly. Three specimens from the eastern side of the loch at Inversnaidsupply the next link in the chain. The first of these (8999, fig. 2, below) is a very siliceous rock, con-sisting chiefly of folia of granulitic quartz with biotite, chloritizedbiotite, albite, and magnetite. The quartz is all recrystallized intoa coarse mosaic, and the albites are larger and more distinct than inthe last specimen; there is also a tendency for the albite-grains to Fig. 2.—Slide No. 8999. [Seen under a 1-inch objective.]. [A highly-crystalline gneiss from Inversnaid, showing the first appearance ofsmall authigenic albites and the leaching-out of quartz into and biotite are also present.] be concentrated in folia. In a more micaceous specimen (9000),chlorite and muscovite are very abundant, being associated bothwith folia of quartz and with the authigenic albites; but thealbites are hardly, if at all, more abundant than in the moresiliceous The third specimen (3680) is composed chieflyof flakes of chlorite and muscovite lying at all angles to the bedding,with interstitial quartz and a few large albites. Thus, in a rockwhich most closely resembles a phyllite or slate in composition, thedevelopment of albite is little greater than in a highly-quartzosegneiss evidently formed from a grit. The albites in these specimensshow little or no trace of idiomorphic outlines: they appear as roundedor elongated grains. Polysyn
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
