Mr Hugh Miller on River- Terr aciiiy. 267 



Prestwich was preceded in this view by Lyell, who held it 

 as early as 1841, and seems to have held it unmodified to 

 the last.* Lyell had early pointed out how streams cross 

 and recross the general line of their descent, levelling out 

 the plains that afterwards form the terraces. ■[- About the 

 time of the Somme controversy, Dana, in America, was 

 working out the same views, and embodying them in the 

 first edition of his Text-Book. | AVhitaker,§ and Foster 

 and Topley, || in England, and, more recently, Milne Home H 

 in Scotland, and Hull ** in Ireland, have also explained the 

 terraces which they have described, by means of successive 

 accelerations in excavating power produced by successive 

 elevations of tlie land, -ff Mr Milne Home in this manner 



Fig. 2. 



Section of a Valley, showing the Formation of River-Terraces during 

 successive elevations of the land (Dana, Manual of Geology, 1863, p. 555). 

 E,^, E,2, R", successive River Channels ; F, F^, F-, successive Flood-Plains. 



interprets the whole interior of the Tweed valley, holding 

 that " as the sea fell from one level to another, so must also 

 the rivers have fallen from one channel to another," even 

 throughout their whole length. 



In Playfair's original sketch it will be noticed that there 

 is no allusion to the sea. Hutton and Playfair were well 

 aware of the existence of raised beaches ; their whole philo- 

 sophy postulated elevation as placing the land within reach 



* Students' Manual of Geology, 1871, p. 78. 



t Principles of Geology, 1830. 



:|: Text-Book of Geology, 1863. 



§ Guide to the Geology of London and Neighbourhood. 



II The Medway Gravels (Quart. Jour. Geol. Soc, vol. xxi. (1865), p. 

 443). 



U Trans. Roy. Soc, Edinb., vol. xxvii. (1875), p. 513. 

 ** Physical Geology and Geography of Ireland, 1878. 



ft And so also Professor Bonney in respect of the Norwegian terraces (Geol. 



p. 239). 



