328 THE BEAUTIES OF NATURE CHAP. 



and striking, have had, after all, comparatively 

 little part in the result. 



The mouths of rivers fall into two princi- 

 pal classes. If we look at any map we cannot 

 but be struck by the fact that some rivers 

 terminate in a delta, some in an estuary. The 

 Thames, for instance, ends in a noble estuary, 

 to which London owes much of its wealth 

 and power. It is obvious that the Thames 

 could not have excavated this estuary while 

 the coast was at its present level. But we 

 know that formerly the land stood higher, 

 that the German Ocean was once dry land, 

 and the Thames, after joining the Rhine, ran 

 northwards, and fell eventually into the Arctic 

 Ocean. The estuary of the Thames, then, 

 dates back to a period when the south-east of 

 England stood at a higher level than the 

 present, and even now the ancient course of 

 the river can be traced by soundings under 

 what is now sea. The sites of present deltas, 

 say of the Nile, were also once under water, 

 and have been gradually reclaimed by the 

 deposits of the river. 



It would indeed be a great mistake to 



