432 MR. G. BARROW ON THE MOINE GNEISSES [Nov. I9O4, 



these patches, as to make it appear that it is on the opposite side of 

 the Limestone to the Parallel-Ban ded Rocks, while, in reality.it is 

 on the same side. The foregoing diagram (fig. 6, p. 431) shows 

 clearly both the deceptive structure and its explanation. 



Similar patches of dark schist occur in Glen Banvie, and of these 

 the most interesting lies next the small mass of hornblende-schist 

 100 yards above the lower bridge, in the Whim Plantation. It 

 consists of two parts : one very dark, with a dead-black film, and a 

 fine grey siliceous schist or granulite. Three microscope-slides were 

 made of the dark portion (10,551-10,553), and these show that part 

 of the rock contains much dark dust, rich red biotite, while epidote 

 and zoisite are abundant along certain lines in an adjacent portion. 

 Another is tougher and darker, intensely chloritic, containing 

 decomposed garnets and a little andalusite ; a third is composed of 

 felted white mica and pale chlorite. The dead-blackness of part 

 of this rock, along with the occurrence of epidote and zoisite along 

 certain lines, suggest that we may have here a representative, 

 though very thin, of the Little Limestone ; for the Little Limestone 

 will be shown later to pass into an epidote-zoisite rock, containing 

 much dark dust, before its outcrop is finally lost. It is the only 

 known occurrence of this dead-black material within a short 

 distance of the actual Moine Gneisses. The rock next it is very 

 fine in grain, and composed of white and dark mica arranged 

 parallel in a fine granular matrix of quartz and felspar. It can 

 be very closely matched from the Honestones and, by its texture, 

 shows how rapidly the rocks become finer in grain as we cross the 

 belt of decreasing crystallization. 



The examination of these patches of schist clearly shows that they 

 belong to different horizons ; not only is there a hiatus at the base 

 of the Main Limestone, but there is also liable to be one at the top 

 of the Moine Gneisses, or the Parallel-Banded Rocks into which they 

 pass. It seems as though, in an area where the originally-coarser 

 material of the Moine Gneisses was deposited, the currents were 

 strong enough, either to prevent the deposition of the fine mud, or 

 to wash it away after it was deposited. Owing to the shifting- 

 nature of the currents, patches of the fine mud were, however, left, 

 and these lie at different horizons. The finest material of all was 

 probably that which formed the Little Limestone and the Twin- 

 Chlorite Rock, and this is the portion of the sequence that is most 

 persistently missing. But, as already stated, the total thickness of 

 the Dark Schist was quite small, and the hiatus is of no great con- 

 sequence. In connection with it, however, we note a remarkable 

 fact : it is succeeded by a limestone, very impure and very variable 

 in composition. Now, at the top of the Upper Lias in East York- 

 shire a similar sifting-away of the fine mud took place, followed 

 by the deposition of a very impure and very variable limestone, now 

 altered to ironstone, the Dogger or base of the Lower Oolites. 

 Proceeding in one direction, the succession beneath this impure 

 limestone becomes complete at Blea Wyke, on the coast south of 

 Robin Hood's Bay. Proceeding in the opposite direction — inland — 



