Vol. 60.] OF THE EAST-CENTRAL HIGHLANDS. 410 



seeu at Gilbert's Bridge, and niarjy other parts of the section already 

 traversed. This, in turn, is succeeded by the Parallel-Banded 

 material (10.556). now obviously an even-banded alternation of fine 

 sandy and muddy sediment. This rock can be at once identified; 

 it is a phase of the Honestones, a well-known member of the 

 Highland Succession. The Limestone itself is of special interest, not 

 only for its beauty, for which it was once so famous, but also from a 

 peculiarity in its composition. It contains a considerable amount 

 of serpentinized forsterite along certain bands. The rock was cut 

 parallel to these bands, so that, when set up, it gives the deceptive 

 appearance of a thick mass of serpentine. A little farther up the 

 river, the thinness of the parallel-banded Honestones allows the 

 white margin of the Quartzite to come into view, and the two are 

 seen folded together again and again, almost to the end of the sharp 

 bend, where the extraordinarily-straight and deep portion of Glen 

 Tilt commences. In this part of the section it will be noted that 

 the Honestones vary somewhat in composition, being slightly more 

 siliceous at one point than at another. They vary also in thickness, 

 and in one place either thin out entirely or become a mere film, so 

 that the margin of the Limestone is almost, if not quite, in contact 

 with the Quartzite. Just before reaching the sharp bend already 

 mentioned, we suddenly come upon a good-sized exposure of the 

 typical bluish-grey Blair-Atholl Limestone, and it seems at first 

 incredible that this can be the same limestone as the one so often 

 referred to ; but in the course of some recent traverses it was 

 clearly proved that they are really one and the same. A little 

 farther up the stream the Limestone is succeeded by the Dark Schist, 

 rich in kyanite, that is so abundant in portions of the Braemar 

 area, and all trace of the Moine Gneisses close to the Limestone has 

 now disappeared. 



This long section thus clearly shows that the parallel-banded 

 Moine Gneisses, as they cross the belt of decreasing crystallization,, 

 not only become less crystalline, but that they gradually change in 

 composition, passing into the ' Honestones," which were originally 

 a finer and more muddy type of sediment, slowly thinning away as 

 they do so. Where present in mass, the original thickness is so 

 enormously increased by folding that only one side (that next the 

 Limestone), whether top or base, can be seen. AYhen, however, 

 they have become very thin, the other side also is visible, and the 

 rock that lies next this is the fine white margin of the Quartzite. It 

 is thus clear that the Moine Gneisses lie between this Limestone and 

 the Quartzite, and that they may be regarded as the flaggy margin 

 of the latter. Sections have been made to illustrate the pro- 

 gressive change in the nature of the original material of the Moine 

 Gneisses. The first (10,555) was taken from the small quarry close 

 to the road, above the junction of Glen Mhairc with the Tilt. It 

 is a fine-grained banded rock, built up of alternate layers of 

 quartzose and grey granulitic gneiss, or perhaps schist, for the 

 decreasing crystallization to the south-east already begins to be noted 

 here. The structure of the part of the rock that has been cut is 



