Reviews — Geological Survey in Scotland. 265 



To the south-east is the complex area bordering the Tilt Valley, 

 where the Perthshire Series of Highland schists is divided by 

 Mr. Barrow into (1) Central Highland quartzite, (2) Honestones or 

 Parallel-banded group, (3) Little limestone (locally the Ti-emolite 

 limestone), (4) Dark schist, (5) Main limestone, and (6) Calc-flintas. 

 The order of succession, ascending or descending, is not known. The 

 quartzite forms mountains, two of which rise to over 3,000 feet, and 

 Mr. Barrow points out that they are " built up by the repeated folding 

 on itself of one bed of sandstone, which cannot have been originally 

 more than 30 feet thick, if so much. In the Benin a Ghlo Mountains 

 the limbs of the folds are absolutely isoclinal, and attain an amplitude 

 of at least 2,300 feet, with a persistent dip of 60 degrees to the 

 south-east. This structure is exactly that produced by the shutting 

 up of the bellows of a concertina, and may be conveniently called 

 ' concertina structure ' ". 



Associated with the Highland schists are certain intrusions of basic 

 igneous rock, epidiorite and hornblende-schist, and intrusions of the 

 older granites. 



A large tract of newer granite forms the Cairngorm Mountains, with 

 Ben Macdui 4,296 feet in elevation, and portions of Mar Forest in 

 the north-east, being a part of "the largest area of continuous high 

 mountain ground in Britain " ; while to the south, and west of the 

 Glen Tilt area with which it is associated, is another tract of the 

 granite, which rises to 3,304 feet in Beinn Dearg and 2,992 feet in 

 Beinn Bhreac. As remarked by Mr. Barrow, " a great historical 

 interest attaches to this intrusion, for it was to the veins proceeding 

 from it, so admirably seen in the Tilt at the old stone bridge above 

 the Forest Lodge, that Hutton so confidently appealed in support of 

 the view of the intrusive nature of granite, which he so ably 

 expounded in his Theory of the EarthP 



In the eastern part of the Cairngorm Mountains the granite, as 

 described by Mr. Cunningham Craig, contains vertical or highly 

 inclined veins of fine-grained material; which is "the chief source of 

 the Cairngorm stones, which were at onetime so much sought after". 

 Various other igneous rocks, including diorites, lamprophyres, felsites, 

 and quartz-porphyries, are described, and their influence on the 

 scenery is pointed out. 



In glancing at the map while perusing the memoir, it becomes 

 evident how strenuous a task must have been the mapping of the 

 rocks, the physical exertion alone being excessively arduous, and the 

 localities where quarters could be obtained being few and lonesome. 

 IS"© doubt the attractions of fishing may have served to relieve the 

 monotony, and rest the individual when stress of weather prohibited 

 field-work. 



Glacial deposits and peat extend over large areas, together with 

 fluvio-glacial gravels (in the Spey Valley) and alluvium. It is 

 remarked by Mr. Hinxman that ""the effect of glacial action in 

 modifying surface features is principally shown by the softened 

 outlines produced by distribution of glacial detritus over the 

 irregularities of the pre-glacial surface". Interesting observations 

 are recorded on the scenery, the river-systems, and the changes they 



