part 2] THE SOUTH-WEST HIGHLAN^DS Or SCOTLAND. 93 



(2) In sucli rocks increasing metamorphism leads from slates and phyllites 

 through mica-schists into either garnetiferous mica-schists or albite-schists. 



(3) In rocks of a different composition (as, for instance, quartzite, lime- 

 stone, or even carbonaceous or calcareous politic sediments) response to 

 metamorphic influences may not agree very closely with what is shown in 

 fig. 3. Thus the Ballachulish Quarries yield black roofing- slate, although 

 situated on the margin of the garnetiferous zone of fig. 3 (1916, p. 202). 



(4) A vague agreement between the outcrops of successive metamorphic 

 and structural zones, respectively, lends distinct support to a theory of 

 metamorphism controlled by depth-temperature, such as was developed by 

 Clough (1897, p. 91) to account for the relatively high metamorphism 

 characteristic of the axial belt of the Cowal Anticline (see figs. 1 & 3). 



(5) The agreement noted above is so incomplete that no increase of 

 metamorphism accompanies the emergence of nappes north-west of the 

 Loch- Awe and Glen-Creran Synclines. This capriciousness suggests recourse 

 to Mr. G. Barrow's theory of metamorphism controlled by temperature 

 dependent upon magmatic distribution (1912 a). To me, there seems to 

 emerge no reason against combining Clough's and Barrow's interpretations. 



(6) Fig. 3 shows sufficiently clearly that crystallization continued until 

 the close, at least, of the main nappe-movements : there are no marked 

 metamorphic inversions. 



(7) Clough did much to distinguish certain mineral developments of Cowal 

 as of pre-anticlinal, or anticlinal, date, respectively (1897). I have now 

 found good evidence of the development of albite in the albite-schists of 

 Cowal during both these periods. As albite -development is due to specialized 

 conditions of regional metamorphism (hydrothermal, according to E. H. 

 Cunningham -Craig, 1904 a, p. 26), it looks as though the early and later 

 movements classified in fig. 1 should be regarded as successive chapters in a 

 long -continued history of mountain-building. Among the products of the 

 later movements is the Loch-Skerrols Thrust, which I correlate with the 

 Moine Thrust of the North-West Highlands. Accordingly, I am led to 

 suspect a fairly close connexion between the south-eastward movement of the 

 great nappes of the South-West Highlands and the north-westward move- 

 ment of their better-known fellows of the North-West Highlands. Naturally, 

 this opens the door for comparison of the Southern Highland nappes with 

 those which will for ever be associated with Tornebohm's name in Scandinavia. 

 Moreover, if one is ready to look beyond the limits of Caledonian time, one is 

 tempted to trace an analogy between the north-westward movement revealed 

 in Islay and the back-movement of the root-region of the Alpine Chain 

 towards the Plain of Lombardy. 



Corrigenda since 1910. 



From 1910 onwards the Greological vSociety has published a 

 series of papers on South-West Highland tectonics, written by 

 myself, and one describing the structure of the Glen Orch}^ district, 

 in which I collaborated with Mr. M. Macgregor. All toJd, these 

 papers cover more than half of the area dealt with on the present 

 occasion. Their detailed descriptions and their beautifully 

 reproduced maps are available to anyone who wishes to realize the 

 full appeal of the interpretations here advanced. It is, therefore, 

 important to assist the reader by enumerating at this juncture 

 such modifications as have come in the wake of our steadily 

 increasing knowledge. 



1910. Recumbent Folds in the Schists of the Scottish 

 Highlands. — This paper deals with the recumbent folds of Ballachulish, 

 Aonach Beag, and Appin, north and west of the granite-mass of Etive ; their 



