Hillside. 1 19 



halations from the cement factories, to reappear again farther 

 to the north, a glittering line of light in the morning sun, as 

 it flows onwards to meet the Thames at Sheerness. 



Did the river really cut its way through these hills until 

 it reached its present level, or did it simply find a natural 

 crack in the rocks through which it took its course ? The 

 latter could hardly have been the case, since the rocks are 

 compact and solid enough, whilst the presence of sand and 

 gravel at varying heights proves that the river has flowed at 

 different levels, and has only gradually reached its present 

 position. In the earlier part of its course the river flows 

 over the AVealden clay, and in the gravel beds which occur 

 along its banks in the lower part of its course, we find stones 

 and other materials which have been brought from this 

 upper part. Seeing that the river runs across the line of 

 direction of the hills, we are forced by these facts to come to 

 the conclusion that it must have cut its way through six 

 hundred feet of chalk, gault, and greensand, in order to 

 reach its existing level, and that the vast quantities of 

 material eroded by its action have contributed to the for- 

 mation of the extensive mud flats now to be found in the 

 tidal areas near its mouth. 



This erosion must have been going on for a very long time. 

 How do we know that ? you ask. Partly from what we 

 know of the slow action of running water and from a 

 comparison of the power at disposal with the work done ; 

 partly, also, because in the old river gravel-beds, to which 

 we have already referred, bones of the elephant and rhir 

 noceros, together with those of many species of animals now 

 extinct, have been discovered; and, finally, because stone 

 implements, which we know were made by a race of human 



