part 2] THE SOUTH-WEST HIGHLANDS OP SCOTLAND. 89 



their upper parts have travelled markedly farther to the north- 

 west than their lower, Charles Callaway clearly realized the 

 significance of this phenomenon (1884a, p. 221), as also did 

 Dr. B. N- Peach & Dr. J. Home, who met its counterpart in 

 another locality (1884 h, p. 34 ; 1907 h, p. 481). 



But such weathercocks are seldom available. More often one 

 has to rely upon the obvious relationship that isoclinal anticlines 

 close in the direction of the movement of which they are a record. 

 Where the folding has not a recumbent tendency, the application 

 of this rule may present no special difficulty. As an example, one 

 may cite the outward movement from the fan-axis of Loch Awe 

 (P. Macnair, B. N. Peach, and others), with which may be 

 grouped the south-eastward movement of the Cowal Anticline 

 (Clough), and the north-westward movement of the Islay Anti- 

 cline (Baile}^). 



In the case of recumbent folds, the recognition of the direction 

 of movement is often more difficult, since the distinction of anti- 

 clines and synclines ma}^ involve careful research. The general rule 

 is that anticlines are characterized by cores of relatively old rocks, 

 and vice versa. Basing m}^ argument upon this rule, I venture to 

 suggest that the recumbent fold of Ben Lui (PL I) is a syncline, 

 which, closing as it does towards the north-west, indicates move- 

 ment towards the south-east. There are, however, a few notable 

 exceptions to the general rule just stated. In 1907, Sarasin & 

 Collet (1907 c, pp. 586-89) explained why they no longer opposed 

 the cumulative evidence of Dr. H. Schardt and Prof. M. Lugeon 

 in regard to the northward movement of the Pre- Alps. Their 

 original difficulty had been the existence in the Zone des Cols of 

 apparently anticlinal folds closing towards the south. They later 

 realized that these folds had been involved in an exceptionally 

 complex series of movements. I should myself describe them as 

 secondary recumbent synclines developed in a sequence previously 

 inverted. 



Fortunately, one is not restricted to age-relationship in the 

 recognition of recumbent anticlines. Clough, for example, de- 

 veloped a most ingenious method of attacking this difficult 

 problem. He found that he could distinguish innumerable 

 diminutive folds of ' pre-anticlinal ' age in Cowal, and that, of 

 these folds, those closing towards the south-east showed a great 

 tendency to have their lower limbs attenuated and correspondingly 

 lengthened (fig. 2, p. 90). On the ground that general experience 

 teaches us that it is anticlines that preferentially exhibit attenua- 

 tion of their lower limbs, Clough identified these south-eastAvard 

 closing folds as anticlines ; from which, of course, he deduced a 

 south-eastward direction for the originating movement. (Like 

 certain other deformational indices, this one, interpreted em- 

 pirically, survives inversion, as the reader will realize if he turns 

 fig. 2 upside down.) 



A difficulty in the way of applying Clough's rule is the fact that 

 in nature the tendency to attenuation is by no means restricted to 



