14 MR. E. H. CUNNINGHAM-CRAIG ON [Feb. I904, 



side have been strongly compressed. The anticline is well-marked 

 by the occurrence of many of the highest hills in the district, as, for 

 example, Beinn Ledi, Beinn Aan, Beinn Yenue, and Beinn Bhreac, 

 which demonstrate the great resistance to denudation that these beds 

 present when vertically folded. A point to be noted in the belt of 

 country containing the anticline is that, although the folding is 

 isoclinal in the low ground, upon the hilltops the folds become 

 shallower and open out, thus showing a vertical gradation from 

 simple flexure to highly-compressed folding. 



North-west of the anticline of Beinn-Ledi Grits comes one of the 

 most important structures in the area, a complex syncline of con- 

 siderable depth which brings down the overlying Green Beds. This 

 structure is traceable from Loch Lomond at Bowardennan, where 

 the trough is shallow, to the Trossachs, where the trough is most 

 clearly marked and deepest. The whole trough, which attains 

 a breadth of 1| miles in places, is marked by the outcrops 

 of the Green Beds, repeated several times — each outcrop being 

 essentially a minor synclinal fold. It was the mapping of these 

 beds, which form an easily recognizable horizon, that first made 

 clear the structure of the district. The folding is still distinctly 

 isoclinal in the lower ground, but less highly compressed towards 

 the hilltops ; while, as we proceed north-westward, the axes of the 

 folds are seen to incline at successively lower angles to the south- 

 east. Thus, as regards the folding, but not the bedding, there 

 is a fairly well-marked fan-structure, which embraces the anticline 

 of the Beinn-Ledi Grits and the syncline of the Green Beds. 



To the north of Loch Katrine this complicated syncline opens out 

 rapidly into a wide shallow basin, somewhat complicated by faulting 

 and overfolding at the south-western edge, where one lip of the basin, 

 as represented by the outcrop of the Green Beds, is repeated' four 

 times in Glen Finglas. On the south-eastern margin of this basin 

 the folds of Green Beds ' pitch out ' towards the hilltops, and the 

 folding, though still sharp, becomes shallow : so that the outcrop is 

 represented by a few corrugated outliers, in which the folding, 

 though acute, is not of sufficient depth to affect the shape of the 

 outlier. Farther to the north-east, where the basin-shape becomes 

 less complicated, the folds open out still more, the strata being 

 flexured into large gentle domes and troughs, while each bed is 

 folded into small corrugated and right-angled folds ; overfolds are 

 infrequent, and when present their axes incline to the north-west. 



South-west of the Green-Bed outcrop in the great syncline the 

 folding is less well-marked and regular, but traces of the trough 

 can be made out on the western side of Loch Lomond. 



The area, amounting to nearly one-third of the whole sheet, to 

 the north-west of the great syncline, does not afford good evidence 

 of folding on a large scale. This is no doubt partly due to the fact 

 that recognizable horizons cannot be followed throughout the area, 

 but it is also certain that through the greater part of this area 

 there is little or none of the regular compressed folding charac- 

 teristic of the belt of country nearer to the Highland Boundary. 



