Vol. 69.] LOCH AWE SYNCLINE (ARGYLLSHIRE). 295 



The examples given above to illustrate the structural relations of 

 the various members of the Loch Awe Group one to the other, and 

 to the Ardrishaig Phyllites below, might doubtless be supplemented, 

 with very little trouble, by further investigation. At the same 

 time, they are regarded as sufficient in themselves. The reader 

 must be warned, however, that he will find in the previous liter- 

 ature many references to ' folds ' pitching in this direction or in 

 that, to ' anticlines' and ' synclines,' to ' inliers ' and ' outliers,' the 

 existence of which, if established, would be fatal to the present 

 interpretation. As a matter of fact, many of these folds, despite 

 their definite designation, are essentially subjective, having been 

 based upon the current reading of the stratigraphical succession. 

 The geological literature of the Highlands has suffered greatly in 

 the past from this subjective presentation of tectonics, for there are 

 very numerous descriptions in which observation and inference have 

 not been at all clearly differentiated. There can be little doubt 

 that this indirect method of approaching tectonics owes much of 

 its fascination to the success with which Prof. Charles Lapworth 

 employed graptolitic zones in the elucidation of the structure of 

 the Southern Uplands. Another point must be borne in mind in 

 dealing with the Loch Awe sequence. The various rock-types, 

 although sufficiently separated to allow of the subdivision of the 

 group, are quite certainly interstratified to a very considerable 

 extent. Thus it happens that in some sections we find folds ex- 

 posed wherein black slate and limestone clearl) r underlie quartzite, 

 and in others precisely the reverse. Such sections, revealing partial 

 sequences, may prove of great service in working out the structure 

 of the locality in which they occur ; but, taken by themselves, 

 they throw no light whatever upon the structural relationships of 

 the major subdivisions of the Loch Awe Group. 



(7) In the Scottish Highlands one should never assume that the 

 order of structural superposition now obtaining is the same as the 

 original order of stratigraphical superposition. In the Loch Awe 

 Syncline, however, there is good reason to believe that the two are 

 in agreement. This evidence is afforded at two localities. 



(7 a) At Kilmory Bay Mr. Grant Wilson found that the Ardri- 

 shaig Phyllites dipped steeply beneath a conglomeratic grit marking 

 the base of the Loch Awe Group [18, p. 64]. The grit is, for the 

 greater part, a pebbly quartzite with bands of fine conglomerate 

 dispersed at intervals throughout. A feature of the conglomerate- 

 bands, which impressed me very strongly, was that each of them 

 has a well-defined base and an ill-defined top ; the pebbles start 

 suddenly in full force at the bottom, and then gradually decrease 

 in number upwards, allowing the conglomerate-bands to merge, in 

 this direction, with the containing quartzite. The tops and bottoms 

 of the conglomerate-seams are thus strongly contrasted, and the 

 contrast is of the type with which one meets, not uncommonly, in 

 unfolded conglomerates. In fact, it is exceedingly difficult to escape 

 the inference that these conglomeratic seams are 'right way up.' 



Q. J. G. S. No. 274. x 



