66 The Sea 
An even coast line may change into an uneven one, or vice 
versa, by a change in the level of the land. Coast lines tend 
to become straight with advancing age. Subterranean forces 
in many portions of the world are constantly changing the 
level of the land so that what may previously have been be- 
low water level may become today’s shore line; or valleys 
high above the sea may be lowered until filled by the sea to 
form long inlets and estuaries. Studies of the topography of 
the ocean bottom reveal in some places great canyons where 
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MUD DISTRIBUTION OF 
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rivers once flowed, submerged mountains, and inundated 
forests. In other regions of the world the remains of marine 
animals are found on mountain tops thousands of feet above 
sea level. All this is evidence of the constant changing of the 
level of the land. 
Of particular interest are the fiords of Norway. Evidence 
points that they were originally valleys carved out of a moun- 
tainous land surface by glaciers, later submerged by a general 
lowering of the land level to form long rock-bound inlets. 
Acting against the process of marine denudation is the 
process of marine deposition which is constantly building 
up the coast lines of the world. Loose materials carried from 
