48 [March 27, 



countries, causing a rise in the rivers of from 10 to 40 feet, and 

 inundating the adjacent valleys. 



Other forces, however, besides an increase in the water-power, 

 seem required to account for the excavation of the great valleys, and 

 the author thinks that cold and ground-ice have performed a very 

 important part in the operation. In support of this view, he adduces 

 the opinion of Arago and the observations of M. Leclercq and Col. 

 Jackson, both of whom show how constantly this ice is formed in 

 cold climates in rivers with stony and gravelly bottoms, such as the 

 old post-pleiocene rivers must have been. Amongst other obser- 

 vations given are those of M. Weitz, who states that in the north 

 of Siberia the formation of ground-ice can be seen in the rivers at a 

 depth of 14 feet and more, and that in "rising from the bottom, 

 the masses of ice bring up with them sand and stones, and let them 

 down at places far distant from whence they came ;" and he concludes, 

 " that not only does the current occasion a change in the bed of the 

 river by its erosion of the looser soil, which it carries from one place 

 to deposit in another, but that the ice, which forms at the bottom 

 of rapid rivers in very cold countries, tends also to effect a change in 

 the beds of those rivers." 



Another agent would co-operate with the last ; this is the freezing 

 of the ground and the rending of rocks by frost. Taking extreme 

 cases, Crantz shows to how great an extent this operates in Green- 

 land ; Dr. Sutherland gives some still more striking instances on the 

 shores of Barrow Strait, and Sir J. Richardson on the Mackenzie 

 River. Even in our country, the disintegration produced during one 

 severe winter on a fresh vertical section of chalk is very striking. 

 A remarkable instance is quoted from Sir R. Murchison's ' Russia,' 

 of a long terrace of angular blocks of limestone broken up and left 

 by the winter-ice 30 feet above the summer level of the Dwina 

 near Archangel. 



With all these combined operations, the author still doubts whether, 

 without an uplifting of the land, the effects in question could have 

 been produced ; and he shows that the coasts of this part of England 

 and France are fringed here and there by a raised beach, which he 

 correlates with the low-level gravel of Abbeville, whilst the high-level 

 gravel of St. Acheul is correlated with beds occupying on the coast 

 a level higher by 50 to 100 feet, marking the difference of level 



