Vol. 60.] OF THE EAST-CENTKAL HIGHLANDS. 447 



It is now recognized that the granulitic gneisses and mica-schists 

 of Moine type cover wide areas of the Highlands, from the north- 

 west of Sutherland and Ross to the Grampians ; and it is further 

 admitted that they represent sediments of siliceous and argillaceous 

 types. The speaker believed that the first part of the paper would 

 form a valuable addition to our knowledge of the petrography 

 of the Moine Gneisses. The second part, dealing with the probable 

 stratigraphical horizon of these altered sediments, raised questions 

 of great interest and importance. Along their north-western 

 margin their boundary is defined by the Moine Thrust, while along 

 their south-eastern limit in the Grampians, where they come into 

 contact with the sedimentary strata of the Eastern Highlands, no such 

 line of disruption had been detected. He agreed with the Author 

 in thinking that no set of faults like that of Glen Tilt and Loch Tay 

 could explain the relationship, for the obvious reason that the 

 Moine Gneisses occur to the south-east of that line of disruption in 

 Perthshire and Aberdeenshire. The Author advanced the ingenious 

 explanation that the Moine Gneisses pass laterally into the Parallel- 

 Banded or Hone-Rock group of the East-Highland sequence which, 

 according to him, lies between the Perthshire Quartzite below and the 

 Little Tremolite-Limestone (or, when the latter is absent, the Blair- 

 Atholl Limestone) above. It had been clearly proved, as contended 

 by the Author, that there is decreasing crystallization of the Moine 

 Gneisses along their south-eastern margin, and it had been further 

 conclusively proved that both the Parallel-Banded series and the 

 Perthshire Quartzite merge into granulitic gneisses along their 

 junction with the Moine Gneisses. Indeed, this feature is so marked 

 that several members of the Geological Survey had drawn a line to 

 guide the colourist, but not a stratigraphical line between theMoine 

 Gneisses to the north and the schistose Dalradian sediments to the 

 south. 



Regarding the section at Gilbert's Bridge, in Glen Tilt, it was 

 doubtless true that a band of limestone with dark schists is there 

 repeatedly infolded with the Moine Gneisses, as the Author showed, 

 and the speaker agreed with him in thinking that it represented the 

 Main Limestone of Blair Atholl. Similar evidence had been obtained 

 in the valley of the Tarf, north of the Tilt ; while north of the Dee 

 the Blair- Atholl Limestone, the Dark Schist, and even the Perthshire 

 Quartzite, had been found within the area of the Moine Gneisses, 

 and infolded with the latter. The Author's reading of the section at 

 Gilbert's Bridge involved his interpretation of the East-Highland or 

 Dalradian sequence. But some of his colleagues had been led by 

 their detailed mapping to the same conclusion as that of Prof. Nicol, 

 namely, that the Perthshire Quartzite overlies the Black Schist with 

 the Little Limestone. The speaker referred to the transgression of 

 the Quartzite and to the evidence furnished by the Boulder-Bed at 

 Newbiggin, south of Braemar, where it rests upon the eroded edges 

 of the Parallel-Banded series, and is folded over an arch of the 

 Tremolite-Limestone. In the opinion of the speaker, the view that 

 the Quartzite is the highest member of the series, although not free 



