16 STUDIES, SCIENTIFIC AND SOCIAL chaf. 



that " valleys of all kinds, from the most open to the 

 most narrow and profound, are hollows worn by erosion," ^ 

 He was struck by the fact of many of the rivers of the 

 south of Ireland, after running for miles over low plains 

 open to the sea, suddenly turning at right angles, cutting 

 through the hills by deep narrow ravines, and so reaching 

 the sea beyond them. Sometimes even the hills the 

 river cut through were isolated, so that the river might, 

 apparently, have passed round them in either direction. 

 The explanation usually offered of these phenomena was 

 that the hills had been fissured by subterranean forces, 

 and that the rivers had taken advantage of them to 

 change their course. But close examination showed that 

 these ravines were not fissures, but channels eroded in 

 the rock, since the solid rock could often be traced un- 

 broken across the very bed of the stream. And, after 

 examining many ravines in different parts of the world, 

 Mr. Beete-Jukes came to what then seemed the very 

 startling conclusion that, except, perhaps, in districts 

 recently convulsed by great earthquakes, there is no such 

 thing as a glen, ravine, or valley occupying the upper 

 portion of an open-mouthed fissure. On the contrary, in 

 every case the whole space between the two sides of the 

 valleys was once filled by rock, which has been gradually 

 worn down and carried away. The very frequent presence 

 of cascades and waterfalls in such ravines, formed by a 

 continuous bed of hard rock crossing the stream, is itself 

 sufficient to disprove the theory of fissures, in which case 

 the whole bed would present a mass of fallen fragments, 

 filled in with pebbles and sand; but this consideration 

 seems never to have occurred to the upholders of the 

 apparently obvious and easy theory of violent disruption. 

 It remains, however, to account for the very common 

 phenomenon of rivers apparently going out of their way 

 to cut a narrow passage through a hill, instead of follow- 

 ing lower ground to a main valley or to the sea. Such 

 in our own country are the small rivers Ouse and Cuck- 

 mere, which cut through the South Downs between 



1 Student' H Manual of Geology. By J. Beete-Jukes, 3rd ed. (edited 

 by Archibald Geikie, F.R.S.), p. 450. 



