24 ON CHANGES IN THE DISPOSITION 



tions, or to meet at right angles ; or for a single valley 

 to be bent, so as almost even to return towards its ori- 

 gin : all of them being cases which no such currents 

 could have produced ; while the simplest case of all 

 is perhaps the most striking. A longitudinal and straight 

 valley originates by a shallow sinuosity, enlarges to 

 a ravine, subsequently to a glen, then becomes a wide 

 open space, and lastly terminates in a plain. It is 

 impossible to imagine a sudden current to produce 

 such a form, nor what its direction could have been. 

 If from the summit, here is a force, and a Body of water, 

 which commence as nothing, terminating, after a pro- 

 gressive increase, in any quantity that can be assigned. 

 If in the opposite direction, the difficulties are such that 

 it really is trifling with a reader to state them ; and as ? 

 in either case, the mass of water is the same through 

 the whole stream, its corrosive power is most exerted 

 where it ought to have acted least, and the reverse. 

 The case of longitudinal valleys opening at the sides, 

 presents another difficulty equally insurmountable. If 

 that of the Dorea has been quoted as an instance, Loch 

 Awe presents one equally striking. There is no possi- 

 ble mode in which a " diluvian current," could have 

 sought and formed a lateral exit through that deep 

 and narrow pass which now gives passage to the Awe. 

 Valleys which have an opening narrower than them- 

 selves, and those containing lakes, where the bottom is 

 lower than the exit and the entrance, are all equally 

 inexplicable on this supposition. The force supposed 

 to have excavated the wide valley of the Tay, could not 

 have left the passes of Craig y Barns and Birnam what 

 they are now ; as Glen Lyon could not even have ex- 

 isted under such a cause ; while the depth of Loch 

 Ness is a sufficient objection, in itself, to the produc- 

 tion of the great Caledonian valley by such a power. 



