Vol. 69.] LOCH AWE SYNCLINE (ARGYLLSHIRE). 297 



and map facing p. 224]. It has long been claimed that Ben Lawers 

 is, in the main, synclinal in structure, and — without entering further 

 upon a subject which needs very careful consideration — it may be 

 admitted, as a working hypothesis, that the Loch Awe Syncline is in 

 part continued through Meall nan Tighearn towards the north-east 

 along the Ben Lawers line. At the same time, it is fairly certain 

 that the Loch Awe Syncline is also continued north-north-east- 

 wards, where it would seem to reappear as the Glen Creran Syncline 

 •on the other side of the granitic complex of Etive. According to 

 this view the Loch Awe Syncline bifurcates, giving rise to the 

 Ben Lawers and Glen Creran branches, which are separated by the 

 -Glen Orchy Anticline recently described by Mr. M. Macgregor and 

 myself [20]. 



It is a familiar fact that the Loch Awe Syncline includes schists 

 ■of an unusually low grade of metamorphism. This point has been 

 very clearly brought out in Mr. Hill's 1S99 paper, so often referred 

 "to already. At the time he contented himself with a description of 

 the phenomenon, without venturing upon any explanation of it. 

 Later, however, he has offered two distinct suggestions of a possible 

 connexion between the metamorphism and the structure of the 

 •district. In the Memoir on Sheet 37 [14, pp. 74, 75], he connected 

 the low metamorphism of the rocks along the central belt with 

 their variable inclination, which latter he regarded as an indica- 

 tion of a less compressed folding in this position than on either 

 side, where steady inward dips predominate. Subsequently, in the 

 Memoir on Sheet 28 [18, pp. 83, 84], he replaced this explanation 

 by one which seems much more likely to be fruitful. Itegional 

 metamorphism, he suggests, is connected both with dynamic action 

 and with depth-temperature ; and accordingly the degree of meta- 

 morphism is likely to correspond, in a broad way, with the depth 

 -at which the deformation was achieved. 



There is, of course, nothing neAv in Mr. Hill's suggestion that 

 depth may have had a determining influence in metamorphism, for 

 this is one of the oldest ideas in Geology. But the theory is none 

 •the worse for being old, and its application in a concrete case is 

 exceedingly welcome. Its probability is considerably enhanced by 

 the following consideration. On the south-east, the Loch Awe 

 Syncline is flanked by the Cowal Anticline, which Mr. Clough has 

 given good reason to believe is an anticlinal structure affecting 

 schists already bent into great recumbent folds. Just as the axial 

 ■belt of the Loch Awe Syncline is characterized by low-grade 

 metamorphism, so that of the Cowal Anticline is characterized 

 by high-grade metamorphism. In discussing this phenomenon 

 Mr. Clough, in 1897 [5, p. 91], pointed out that the rocks at 

 present exposed in the centre of the anticline 



' must, before the ridging up, and subsequent denudation, have been lying under 

 a much greater thickness of rock, and therefore presumably exposed to higher 

 temperatures, derived from the earth's internal heat, than those now occurring 

 far away on the flanks.' 



In this opinion Mr. Clough was, to some extent, anticipated by 



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