C— GEOLOGY. 63 



(2) Clough, Cramptou and Flett have described a wonderful aureole 

 of contact-metamorphism partially surrounding the Inchbae augcn- 

 gneiss of Ross-shire. The history of the district is as follows : A great 

 thickness of sediments accumulated ; a large mass of porphyritic granite 

 intruded into these sediments and hornfelsed them for a considerable 

 distance from the contact ; the whole, at some later period, became 

 involved in conditions of stress and temperature suitable for high-grade 

 regional metamorphism ; the unbaked sediments yielded and were altered 

 to para-gneisses ; even the porphyritic granite was for the most part 

 changed to augen-gneiss ; but the hornfelsed sediments in large measure 

 moved en masse without internal deformation, so that, though crystalline, 

 they retain to this day many of the minutiae of their original structure, 

 such as grains, bedding, ripple marks and suncracks. 



(3) Continuing the work of Clough and Maufe, I have been fortunate 

 enough to trace out refolded recumbent folds in several districts of the 

 Southern Highlands. These folds are many miles in cross-strike extent, 

 and their limbs have suffered inevitable disruption with the production of 

 fold-faults or ' slides.' The investigation of these structures was begun 

 at Ballachulish and has since proceeded far across the country. The 

 available evidence has not in any way been exhausted, and the promise 

 of future discoveries is extremely bright, especially towards Banffshire 

 where Read is at present working. 



The Caledonian portion of the Scottish Highlands is 120 miles broad 

 in the east, but narrows greatly towards the west. Its north-west border 

 is furnished by the Moine thrust-zone. It will be convenient to defer 

 consideration of this great structure-line until we have taken a brief look 

 at the Scandinavian development of the Caledonian Chain, for in many 

 respects the Moine thrust-zone and its foreland belong rather to American 

 geology than to European. 



The most impressive geological phenomenon in Scandinavia is the 

 marginal over-riding of Baltica by the Caledonian mountains. In Britain, 

 where the Welsh Border shows the contact of these two structural elements, 

 it is a mere matter of foot-hills grading into foreland, it is an affair of 

 outposts. True, the Carmel Head Thrust of Anglesey is an important 

 structure of post-Llandovery pre-Devonian date — Greenly gives it three 

 miles of displacement as a minimum and twenty miles as a probability — 

 but this thrust is separated from Baltica by the Welsh zone of folding. In 

 Scandinavia the mountains often appear with startling abruptness, thrust 

 far out over the edge of Baltica. 



The type district for studying the great Scandinavian overthrust is 

 the province of Jamtland. Here comparatively wide exposures of fossili- 

 ferous Cambrian, Ordovician and Silurian pass north-westwards below the 

 over-riding mountains. In the south-eastern part of their outcrop, the 

 Cambrian and Ordovician total only about 300 feet in thickness, of which 

 the greater part is Orthoceras-limestone of Middle Ordovician age ; and 

 the Silurian also is of very moderate dimensions. North-westwards, that 

 is towards and under the moimtains, the Cambrian and Ordovician swell 

 mightily, and show an accession of sandy material which is reminiscent of 

 the north-westward facies-change traced by Lapworth in the Southern 

 Uplands of Scotland, although, of course, the position relative to the 

 Caledonian margin is very different. 



