l62 



THE NATURE BOOK 



ITS BED IS ON ROCK AND CLEAN FROM SAND." 

 The Strid : Wharfedale. 



the V facing the sea, the Mersey is bottle- 

 shaped, three to four miles wide inland, and 

 the neck of the bottle, less than a mile 

 wide, is turned seawards. So it happens 

 that Chester, once a flourishing port, has 

 lost its former importance in this respect. 

 Only vessels of small tonnage can approach 

 its wharves, 

 and these only 

 at high water, 

 whereas Liver- 

 pool has become 

 the great gate- 

 way to the West, 

 and the largest 

 vessels afloat can 

 enter its docks. 



Now let us con- 

 sider what would 

 happen if the 

 river on entering 

 the sea were not 

 subject to tidal 

 influences, or if 

 the tides were 

 feeble as com- 

 pared with the 

 current of the 

 river. Such con- 

 ditions are found 

 in the Mediterra- 



nean. The waste 

 brought down by 

 the Rhone, the 

 Po. and the Nile 

 does not get re- 

 distributed by 

 tidal action, but 

 falls to the bot- 

 tom of the sea 

 when it meets 

 the salt water. 

 Thus vast quan- 

 tities of sand and 

 m u d are c o n - 

 stantly tipped 

 over the banks 

 which form at 

 the mouths of 

 these rivers. 

 These banks grow 

 outwards like a 

 fan, and in the 

 end form lovv% 

 swampy deltas, 

 traversed by 

 " distributaries," which radiate from the 

 point at which the delta first began to 

 accumulate. The amount of material 

 brought down by rivers varies with the 

 seasons. When the Nile is in flood, the 

 water which passes through Cairo is like 

 chocolate in colour. The Yellow River 



THE I'LAINS 



INCAPABLE OF CAKK^LNG ANYTHING 

 FINEST MUD IN SUSPENSION." 

 View on the River Sulby above Greenland Bridge. 



THE 



