TERRACED SLOPES IN NORTH TYNEDALE. 43 



these parallel ledges be attributed — that they are wholly artifi- 

 cial, and not natural in their origin.''' They would remark that 

 the terraces of the kind now under consideration are unlike those 

 of the Glen Roy and the Fluviatile terraces of gravel, as in the 

 Somme valley, and elsewhere ; the Results being too small for 

 such mighty efiicient causes. They would point to the physical 

 features of this district of Western Northumberland as marked 

 by all the peculiarities of the carboniferous or mountain lime- 

 stone formations, its alternations of harder and softer strata, its 

 protruded basaltic crags and conical heights, and freestone or 

 limestone headlands and escarpments, superimposed upon or un- 

 derlying its coals, shales, ironstones, and clays. And they would 

 ask us to account for the comparatively small number of the ter- 

 races under such favourable conditions — why both sides of the 

 valley and of the transverse dales had not been furrowed in more 

 places, and along a greater extent of the hill-sides than we find 

 them, as at Warden Hill and Buteland ridge. They might rea- 

 sonably desire to know how in each lake of the North Tynedale 

 chain in the glacial period the various series of terraces are at 

 different relatwe levels from each other. And above all, why we 

 find the separate ledges dipping out of the horizontal line so 

 much as they do, as in the Birtley example ; and, not only ceas- 

 ing to retain their parallelism, but actually inosculating and run- 

 ning into each other, which is the case in almost every instance. 

 Such arguments must necessarily have great force. Looking at 

 the most striking series of these ledges, that near Birtley, no one 

 could avoid being struck with its very artificial character. It is 

 manifest at a glance. Why, then, were they formed by man's 



♦Compare, however, Mr. Tate's remarks on the Ilumbledon Heugh terraces (Proceedings 

 of Ber. Nat. Club, Vol. IV., p. 160) which I have seen since writing the above. In this par- 

 ticular case he says, — "Such places near the hough have been fui-ther levelled and trimmed 

 by art and used by the early inhabitants of the district for the purposes of cultivation." The 

 reference is to the terraces formed on gravel at the base of the porphyry hills along the shores 

 of the valley of the Till, which appeared as the land emerged from the waters of that estu- 

 ary. It is, perhaps, probable that in a few instances of this kind a natural origin of tciTaccd 

 ledges may be found, as a friend has suggested to me, in a sudden fall, or succession of falls, 

 or depressions of the face of an escarpment from the percolation of water beneath the soil, 

 or underlying strata. On a small scale, tlic action of such quicksaiids is often observable on 

 the slopes of railway cuttings and cmb.inkments. 



