Reviews — Geology of Mid-Strathspey and Strathdeam. 281 



thirty odd pages the authors have condensed, with admirable clarity, 

 an immense amount of information ; it will he difficult to find a more 

 weighty geological pennyworth. 



IV. — Memoirs of the Geological Survey of Scotland. 

 The Geology of Mid-Strathspey and Strathdearn. Explanation 



of Sheet 74. By L. W. Hinxman, E. M. Anderson, and others. 



pp. 97. Edinburgh, 1915; published by Wvman & Sons, Ltd., 



London, E.C. Price 2s. 6d. net. 

 TT1HIS is a continuation of the fine series of Survey memoirs on 

 1 what is perhaps the most minutely mapped and described region 

 of ancient rocks in the world. The area of 432 square miles dealt 

 with lies almost wholly within the county of Inverness, and most of 

 it is devoted entirely to sport. The country is mountainous and 

 belongs mostly to the dissected plateau of the Highlands, of which 

 the Monadhliath Mountains is a comparatively undissected portion, 

 Teaching 3,000 feet in height. To the south-east a part of the great 

 'monadnock ' of the Cairngorm Mountains, with a mean elevation of 

 3,500 feet, rises out of the plateau surface. Three great river valleys, 

 the Spey, Findhorn, and Nairn, cut across the plateau in a N.N.E. 

 direction, of which the first two are certainly of pre-Devonian age. 



The area is entirely underlain by the ancient metamorphic rocks 

 of the Highlands and the igneous intrusions associated with them. 

 Most of the metamorphic rocks belong to one or other of the main 

 groups of the Moine Series, which are classified as pelitic schist and 

 gneiss, siliceous schist and granulite, quartzite, limestone, and calc- 

 silicate rock. These form the lower moorlands of the central and 

 north-eastern parts of the area. Rocks which, owing to rapid 

 alternations of lithological character, cannot be assigned to any of 

 the above groups, and are classed as undifferentiated schists of the 

 Moine Series, occupy the area around the southern granite masses, 

 and form bands across the western and south-western parts of the 

 region. A small area in the neighbourhood of Grantown is occupied 

 by rocks which have a closer lithological affinity with those of the 

 Central Highland or Banffshire Series, and are accordingly separated 

 under the provisional name of the Grantown group. These various 

 metamorphic rocks are fully described under their respective districts. 

 Igneous rocks which have been involved in the foliation are sparse, 

 and are represented only by thin sills of epidiorite and hornblende 

 schist. The three great granite masses of the Cairngorm Mountains, 

 the Monadhliath Mountains, and Strathdearn belong to the Newer 

 Granite period of intrusion (Old Red Sandstone), and are of post- 

 foliation date. Two or three small bosses appear through the gravels 

 of the Spey valley. The view that all these separate masses are 

 continuous at varying depths beneath the roof of schist is supported 

 by the petrographical identity of the several outcrops, the extensive 

 granitization of the intervening areas of schist, and the behaviour of 

 the outcrops in relation to the form of the ground. It is far more 

 probable, however, that the mass is of batholithic habit, rather than 

 thatitis a "large branching luccolite . . . whose irregular upper surface 



