536 River Terraces. 



minor stream in Derbyshire, Lancashire, and Yorkshire, 

 and on the Thames, on the banks of its long sweep- 

 ing curves where it passes through the Cretaceous es- 

 carpment between Appleford and Wallingford. In 

 this way rivers must act and have always acted. It was 

 during a residence on the banks of the Moselle in 1860 

 that I first learned this lesson. 



On the banks of the Thames below Maidenhead, and 

 on those of many other rivers, there are frequent ter- 

 races, often cut out in more ancient gravels, which it 

 had previously deposited. This is one of the effects of 

 the past and present progressive action of rivers, close 

 to or at various distances from any river as it now 

 exists, according to its size and other circumstances. 

 Sometimes these terraces have even been cut in solid 

 rock, but more frequently in Boulder-clay, or in old 

 gravels. Cases such as the following are frequent. The 

 hills or tablelands on either side are, perhaps, made of 

 solid rock, and the terraces lying between the higher 

 slopes and the rivers consist of gravel of comparatively 

 old date. The river at one time flowed over the top 

 of the highest gravel terrace, and winding about from 

 side to side of the valley, and cutting away detritus, it 

 formed the terraces one after another, the terrace on 

 the highest level being of oldest date, and that on the 

 lowest level, that bounds the modern alluvium, the 

 latest. 



Thus, in the following figure, No. 1 represents the 

 solid rocks of a country, covered on the top of the 

 tableland with Boulder-clay, No. 2, these bounding a 

 wide valley partly filled with ancient gravel, No. 3, 

 which originally filled the valley from side to side as 

 high as the uppermost dotted line, 4 ; but a river flow- 

 ing through, by degrees bore part of the loose detritus 



