fTRANSACTlONS OP SECTION C. 623 



b 



to Skye, we enter the wide domain of the metamorphic rocks of the Iligblands, a 

 region now under investigation, and which presents difficult problems for solution. 

 Two prominent types of crystalline schists (Caledonian series, Callaway, and Moine 

 schists of the Geological Survey) have been traced over wide areas in the counties 

 of Sutherland, Ross, and Inverness, and across the Great Glen to the northern 

 slopes of the Grampians. Consisting of grauulitic quartzose schists and muscovite- 

 biotite schist or gneiss, they appear to be of sedimentary origin, though crystalline. 

 They are associated with recognisable masses of Lewisian gneiss covering many 

 square miles of ground and presenting many of the structures so characteristic of 

 that complex in the undisturbed areas already described. Within the belt of 

 Lewisian gneiss at Glenelg Mr. Clough has mapped a series of rocks presumably of 

 sedimentary origin, including graphitic schists, mica schists, and limestones, but the 

 gneiss with which they are associated possesses grauulitic structure like that of the 

 adjoining Moine schists.' Further, in the east of Sutherland, and also in the 

 county of Ross, foliated and massive granites appear which are interleaved in the 

 adjoining Moine schists, forming injection gneisses and producing contact meta- 

 morphism.- 



In the Eastern Highlands the Moine series disappears and is replaced by a 

 broad development of schists, admittedly of sedimentary origin, which have been 

 termed the Dalradian series by Sir A. Geilde. Within recent years it has been 

 divided into certain rock-groups which have been traced by the Geological 

 Survey from the counties of Banft" and Aberdeen to Kintyre. It has been found 

 that, though highly crystalline in certain areas, they pass along the strike into 

 comparatively unaltered sediments, as proved by Mr. Hill in the neighbourhood of 

 Loch Awe.^ " Before the planes of schistosity were developed in these Dalradian 

 schists they were pierced by sills of basic rock (gabbro and epidiorite) and acid 

 material (granite), both of which must have shared in the movements that affected 

 the schists, as they merge respectively into hornblende schists and foliated granite 

 or biotite gneiss. Both seem to have developed contact metamorphism ; indeed, 

 ]\Ir. Barrow * contends that the regional metamorphism so prominent in the south- 

 east Highlands is mainly, if not wholly, due to the intrusion of an early granite 

 magma, now exposed at the suriace in the form of looal bosses of granite and 

 isolated veins of pegmatite. 



The age of the Dalradian schists has not been determined. Though there 

 seems to be an apparent order of superposition, in this series it is still uncertain 

 whether that implies the original sequence of deposition. Since Sir A, Geikie 

 applied the term Dalradian to the Eastern Highland schists in 1891, ' evidence has 

 been obtained " that suggests the correlation of certain rocks along the Highland 

 border with the Arenig and younger Silurian strata of the Southern Uplands. 

 Consisting of epidiorite, chlorite schist, radiolarian cherts, black shales, grits, and 

 limestone, they have been traced at intervals from Arran to Kincardineshire. In 

 the latter region Mr. Barrow contends that they are separated by a line of dis- 

 ruption from the Highland schists to the north ; but no such discordance has been 

 detected in the Callander district or in Arran. Though these rocks of the High- 

 land border have been much deformed, yet their occurrence in the same order of 

 succession in that region and in the Southern Uplands is presumptive evidence for 

 their correlation. 



In view of this evidence it is not improbable that the Dalradian series may 

 contain rock-groups belonging to different geological systems. Indeed, the result 

 of recent Survey work in Islay tends to support this view. For in the south-west 



' Summary of Progress of the Geological Survey for 1897, p. 37. 

 - ' On Foliated Granites and their Kelations to the Crystalline Schists in Eastern 

 Sutherland,' Quart. Journ. Geol. Soc., vol. lii. p. 633. 



^ Aiinnal Peport of the Geological Survey for 1893, p. 265. 



* 'Intrusion of Muscovite-biotite Gneiss in the South-east Highlands and its 

 accompanying Metamorphism,' Quart. Journ. Geol. Soc, vol. xlix, p. 330. 



* Quart. Journ. Geol. Soc, vol. xlvii. p. 72. 



« Annual Report of the Geological Survey for 1893, p. 266 for 1895, p. 25 ; for 

 1896, p. 27. 



