444 Jukes — On the Gorge of the Avon. 



to believe that such rocks have been formed by the melting up of a 

 mere mechanical aggregate of rock-debris, possessing no analogy 

 whatsoever, and whose chemical composition, etc., is known to vary 

 to the widest imaginable extremes. 



In conclusion the author cannot but express his feeling that it is 

 doing an injustice to the memory of such noble minds as Hutton, 

 Playfair, Hall, Humboldt, Von Buch, and others, to bring against 

 them the narrow-minded charge of their wishing to create the earth 

 " entirely by fire." ^ Their writings abound in evidence proving 

 that they never overlooked the all important agency of water in 

 nature's operations, and when claiming for igneous action its true 

 share they based their plutonic theory upon the study of such 

 agency as is exemplified in volcanos, in which, from the first, the 

 co-operation of water (although in some, at that time, incompre- 

 hensible manner) was acknowledged ; and not upon any idea of 

 " dry fusion," which could only have originated in the brains of 

 their antagonists.^ 



n. — On the Gorge of the Avon, at Clifton. 

 By J. Beete Jukes, F.R.S. 



I OBTAINED, the other day, on my way into South Devon, another 

 peep at the Bristol Channel, and the gorge of the Avon, at 

 Clifton, which I had long been wishing for. It showed me, as 

 I anticipated, that the hypothesis of atmospheric erosion, which 

 I was compelled to adopt, a year or two ago, to explain the formation 

 of the river valleys of the South of Ireland, is applicable to the 

 Clifton gorge as to all other similar places. 



With the existing form of the ground traversed by the Avon, 

 above Bristol, it would, of course, be quite impossible for the river 

 to cut a channel across the Clifton Downs. Fill up the gorge of the 

 Avon with the mass of Carboniferous Limestone and Old Eed Sand- 

 stone, that once occupied it, or even half fill it, and the waters 

 of the Avon, after forming a lake, would, long before they overtopped 

 that dam, run into the sea by Nailsea, as pointed out by Sir H. T. 

 De la Beche. 



This, however, only shows that the surface over which the Avon 

 originally ran into the Severn, was not the present surface. All the 

 rivers originally ran over a surface considerably above the present 

 one, and they have continued to run in the same courses during all 

 the wasting of the rock, by which the old surface has been trans- 

 formed into the present one. 



The rivers have been, at once, the channels by which the eroded 

 matter was removed, and the motive power of the eroding machinery. 



Colonel George Greenwood's phrase of " Eain and Eivers," gives 

 us the whole secret in three words. 



1 Apparently an application of the " sensation " principle to geology. 



2 It is nearly half a century ago since Scrope not only pointed out the important 

 part played by water in volcanic action, hut further expatiated upon the difference 

 between volcanic fusion and ordinary melting. 



