400 MR. G. BARROW ON THE MOINE GNEISSES [Nov. 1 904, 



30. On the Moine Gneisses of the East-Central Highlands and 

 their Position in the Highland Sequence. 1 By George 

 Barrow, Esq., F.G.S. (Read March 23rd, 1904.) 



[Plates XXXIII-XXXVII] 



Contents. 



Page 



I. Introduction 400 



II. The Moine Gneisses 400 



III. Mode of Ending-off of the Moine Gneisses 415 



IV. Appendix 442 



I. Introduction. 



The object of this paper is : First, to describe the Moine Gneisses in 

 Perthshire and Aberdeenshire, and to show that in their mode of 

 occurrence and field-characters, as well as in their composition and 

 microscopic structures, they are identical with the Moine Gneisses of 

 the North-Western Highlands. 



Secondly, to trace the mode of ending-off of these gneisses, and 

 to show that, while retaining their characteristic parallel banding 

 they pass into a small zone of rocks, locally known as the 

 Hon est ones, which, in varying phases, lie persistently for miles 

 on the white margin of the Central-Highland Quartzite. The 

 parallel-banded Moine Gneisses are, in fact, simply 

 the flaggy margin of this Quartzite. 



Thirdly, to show, that in this special area, as the flaggy rocks 

 thicken, there is usually a small hiatus in the succession, owing 

 either to the contemporaneous erosion of the finer material that 

 should lie next them, or to its non-deposition. When this parallel- 

 banded material, however, attains a certain degree of fineness, this 

 erosion rarely occurs, and then the other limit of the group is the 

 Little Limestone. In fact, when the succession is complete, the 

 Moine Gneisses can be shown to pass laterally into the rocks of 

 the Honestone Group, and to lie between the white margin of the 

 Quartzite and the Little Limestone. 



Whether these flaggy rocks lie above or below the Quartzite is at 

 present a matter of dispute. The view here taken is that they come 

 above the Quartzite, and the evidence for that view will be given 

 in detail. 



The area examined extends from the River Garry, between Blair 

 Atholl and the summit of the Highland Railway, in a north-easterly 

 and easterly direction to Glen Girnoch, east of Balmoral in 

 Aberdeenshire, a distance of some 50 miles. 



II. The Moine Gneisses. 



The district over which the undoubted Moine Gneisses occur may 

 be divided into three parts : («) the Struan area, which lies to the 



1 Communicated by permission of the Director of H.M. Geological Survey. 



