PORT ECONOMICS 
Then, many rivers are afflicted at their mouths with 
what are termed Bars, i.e. ridges of material which are 
due to various causes, some of them obscure, resulting 
in a diminution of depth of water at the very threshold 
of the port. Immense sums of money have been expended 
in dredging operations at notable ports throughout the 
world with a view to the removal of these bars, or, at any 
rate, to a lowering of their crests. At Liverpool, since 
the year 1890, when dredging operations were commenced, 
no less than 400 million tons of sand have been removed 
from the bar of the Mersey and the approach channels to 
the port; the operation is necessarily continuous, since 
the bar tends to reform. At the mouths of the Mississippi, 
of the Danube, of the Volga and other rivers, extensive 
dredging has been necessary for the same reason. 
At other river mouths, where bars are not definitely in 
evidence, there are shoals and banks of mud and sand 
which impede the channels and dredging has frequently 
to be resorted to for their removal. The entrances to the 
ports of London, New York and Hamburg may be quoted 
as examples. 
All these considerations go to show that no situation 
of a port from a physical point of view can be considered 
as altogether perfect, and in each case the best has to be 
made of the circumstances which obtain. 
HINTERLANDS 
But the outstanding fact is, that the ports have their 
inception and tend to develop, solely in accordance with 
the dictates of trade requirements, along the line of 
recognized traffic routes, and no amount of convenience 
and suitability will originate and foster a port where the 
inducement of trade is lacking. There are plenty of 
harbours and coastal inlets where ports could be established 
with the requisite degree of shelter and accommodation, 
were it not that the absence of conditions favourable 
to trade militate against the attraction of shipping. 
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