406 G. Hlclding — Old Red Sandstone of Forfarshire. 



not here concerned with. In view of what has already been said 

 regarding the tectonic and geogi'aphical relations of these deposits, it 

 can, I think, scarcely be doubted that the peculiar conditions which 

 led to the formation of this rock-type here were in the main con- 

 temporary with the corresponding conditions in Fife and the Carse of 

 Gowrie. It would be foolish to contend that the base of these outliers 

 is on precisely the same horizon as the base of the series in other 

 localities, but I think it must be admitted that these rocks are of 

 Upper Old Red age, which is the only point of importance. 



The Unconformity between the Upper and Loaver Old Rkd. 



Having now examined the evidence proving that these outliers are 

 of the same age as the typical Upper Old Red of Fife, we may 

 profitably examine more fully the relation of the deposit to the Lower 

 series, where it is so admirably displayed in the cliffs of Arbroath. 



The accompanying sketch-map shows, in addition to the main mass 

 of the deposit let in between a pair of faults, numerous small patches 

 which lie undisturbed in depressions in the ancient surface of the 

 Lower Old Red. The actual junctions of the Upper and Lower series 

 are, moreover, exposed in numerous places, and thus a very fair idea 

 of the old surface may be obtained. In the south-west of the map, on 

 the foreshore opposite Victoria Park, the junction may be traced right 

 across the shore, the Upper beds sometimes abutting against a vertical 

 face of the Lower, while in other places they extend horizontally over 

 them. At "Whiting Ness, again, the junction maybe traced for several 

 hundred yards in the foot of the cliff and on the sliore. The surface 

 of contact is nearly horizontal and fairly even until the eastern limit of 

 the Upper beds is reached, where they end off against a high bank of 

 the Lower strata, which is cut in section by the present cliff and rises 

 its whole height (PI. XX, Pig. 1). In the base of the Upper beds west 

 of the foot of this old bank, angular blocks of the sandstones of the 

 Lower series more than a yard in length are included. Another fine 

 example of the Upper series resting against a steep bank of the Lower 

 is to be seen at Seaton Point, where the main fault forming the north- 

 west boundary of the former is also admirably exposed (Fig. 2), the 

 Dark Cave being drilled through the Point along it. On the east side 

 of Dickmont's Den two troughs cut out in the Lower beds are seen in 

 section in the cliff filled in with the conglomerates of the Upper series. 

 But by far the finest example of a valley cut in the older series is to 

 be seen in an inlet in the cliff in the extreme north-east of the map, 

 and on the west side of Lud Castle (just off the map). There the 

 horizontal Upper beds fill a V-shaped depression over 100 feet in depth. 



It appears from these instances — and others might be added — 

 that the old surface on which this mass of Upper Old Red rests is 

 a distinctly irregular one, in every Avay a typical old land-surface. 



This fact is of considerable value in estimating the significance of 

 this unconformity. Those wishing to minimise the importance of this 

 break might suggest that the folding and erosion of the Lower Old 

 Red proceeded pari passu with its deposition, and that though the 

 break appears great where the Upper series oversteps on to the lower 

 beds of the Lower series, in the centre of the anticline, yet the 



