442 MR. G. BARROW ON THE MOINE GNEISSES [Nov. I904, 



becomes clear. While the coarser material is deposited within 

 these fans in wet periods, in dry the line of deposition of finer 

 material would penetrate far within the fans (or towards the 

 shore-line), and thus the coarser material within them would 

 be separated by these films at more or less regular intervals. 

 The origin of the flaggy aspect of the typical colour-banded gneisses 

 is thus accounted for. In this investigation we have been dealing 

 with the phenomena along the margin of one of the larger fans ; 

 but the identity of the Moine Gneisses over large areas makes it 

 clear that there must be several larger fans. 



Briefly, then, the Moine Gneisses are simply' the flaggy 

 top of the Central-Highland Quartzite: this flaggy top is 

 restricted to certain larger fans of deposition. As we approach 

 the margin of each fan, the flaggy material becomes of a more 

 muddy nature originally ; and while the typical parallel banding- 

 is retained, it becomes very much finer and the whole bed thinner. 

 It is to the fact that this change in original composition has not 

 been hitherto quite fully grasped, that the difficulty in accounting 

 for the disappearance of the gneisses is essentially due. 



IV. Appendix. 



A peculiar interest attaches to the easily-identified phases of the 

 Felspar-Eock of Glen Callatcr, as by means of them it can be proved 

 that the great masses of newer granite, shown on a geological map 

 of this area, have rarely produced any serious effect on the already- 

 metamorphosed Highland rocks. The following series of slides (as 

 well as a number of others) was cut so as to put this fact beyond 

 dispute, as well as to identify the zone in the Dark Schist. 



10.777. Quarter of a mile north of Druid Farm, above Killiecrankie, and north- 



west of Ben Vrackie. Perth ; 1 -inch-sheet 55. 

 9454. Near the head of the Tilt, north of Falar. Perth ; Sheet 64. 



8548. Near the head of Glen Choinnich, one of the branches of the Ev Burn. 

 A branch of the Dee above Braemar. Aberdeen ; Sheet 64. 



10.778. Glen Ey, below Aucherrie. Aberdeen ; Sheet 65. 



3455. Glen Callater, just outside the Lochnagar Granite. South of Braemar. 



Aberdeen ; Sheet 65. 

 71)75. A small patch of Dark Schist, completely enveloped in the Lochnagar 



Granite. Close to the last. 



The Lochnagar Granite is 10 miles in diameter, yet this inclusion 

 of the Felspar- liock does not appreciably differ from any of the 

 others. The first specimen was taken 25 miles from this inclusion, 

 and there is no newer granite anywhere near it. Thus it is evident 

 that the great mass of the Lochnagar intrusion has produced 

 practically no effect on the already-altered Highland rocks. 

 All these specimens have been taken from the south side of the 

 great belt of increasing metamorphism. 



On the north side of the belt similar phenomena are observed. 

 Here the original chloritic material is absorbed in the formation of 

 cordierite, but if the right portion of the Dark Schist be selected, 



