816 TYTs^EDALE ESCARPMENTS; 



*' rig-and-fur." The larger streams, however, are less influenced 

 by it. Some, indeed, such as the Haltwhistle Burn (Caw Burn) 

 below Greenlee Lough, and the Simondbum below Townshields, 

 occupy single grooves for long distances ; but sooner or later they 

 are apt to be found shunting, as it were, their line of flow. There 

 are those, like the Knag Burn, that cross the ridges almost as 

 if ignoring their presence, not a little resembling, with their 

 furrow-guided feeders, trees with their branches trained along 

 espaliers; and there are others, again, intermediate in character, — 

 notably the Simondburn in its upper reaches, — which bend in a 

 series of zig-zags composed of longer furrow-guided lines, and 

 shorter gap -traversing ones. Most of the numerous streams that 

 enter I^orth Tyne between the Simondburn and the Houxty Burn 

 have, as already partly indicated, worked into the trend of the 

 ridges ; presenting, in their general parallelism, a complete con- 

 trast to the unrestrained ramifying of Chirdon and Smale Burns 

 further north. In this they seem to have only followed the 

 general gradient ; and, taking the region as a whole, obedience 

 to the general gradient is the rule. 



What is thie interpretation of these facts ? The streams, we 

 see, are not absolutely coerced into single lines of furrow, but 

 frequently break across through gaps. jSTow, before the true 

 character of Escarpments was recognised, the question was suffi- 

 ciently answered by supposing the narrow breaks giving passage 

 to streams to have been open flssures, or low-lying points at 

 which lakes ponded up among the ridges had overflowed and 

 drained. Jukes, however, recognising, in the South of Ireland, 

 as Ramsay, at the same time, was recognising in the South of 

 England, that the gaps are not in lines of fissure, and not in 

 positions where, barred by them, the stream would have chosen 

 to run, concluded that their excision was accomplished pari 

 passu with the formation of the ridges themselves; in other 

 words, that the streams had flowed there before the ridges came 

 into existence.* 



* Jukes' River Valleys of South Ireland, Quart. Journal Geol. Soc, Vol. XVIII. Also 

 Jukes and Geikie's Manual of Geol., p. 4-54. A vigorous sketch of the behaviour of these 

 Irish Rivers is given in Hull's Physical Geol. and Geog. of Ireland, 1878. 



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