STRUCTURE AND SURFACE FEATURES 423 
seen, occur in dry regions, where river-action is at a 
minimum, and where consequently the depressions caused 
by crustal deformation persist either as dry or only partially 
filled basins. The rate of subsidence has exceeded the rate 
of sedimentation, and as the lakes seldom or never overflow, 
save only in very wet years, their rims are not cut down by 
river-erosion. The large lakes of Northern Europe and 
North America are also tectonic basins, largely modified, 
however, by glacial erosion and accumulation. They prob- 
ably came into existence underneath the great ice-sheets 
which formerly covered those regions, and at a time, there- 
fore, when ordinary fluviatile action was largely in abey- 
ance. They could neither be silted up by sedimentation, 
nor breached by the action of outflowing water, and too 
short a time has elapsed since the glacial period to allow of 
their obliteration by these causes. In well-watered regions 
all depressions of the surface, whatsoever their origin may 
be, must sooner or later disappear—the beautiful lakes of 
our temperate lands and mountain areas are merely 
evanescent features. 
5. COAST-LINES 
The coast-lines of the globe are the joint-product of 
hypogene and epigene action. ‘Their general trend is mainly 
due to crustal movement, and is naturally determined by the 
position of the continents in relation to the great oceanic 
depression. The former are nowhere co-extensive with the 
true continental plateau, considerable areas of which in many 
parts of the world are below the sea-level. When the 
continental coast-lines approach the margin of that plateau, 
they usually continue for long distances in one direction, are 
rarely much indented, and show few or no fringing islands. 
enversely, when they recede from the edge of the 
continental plateau, their trend becomes irregular, numerous 
inlets appear, and marginal islands often abound. A highly 
indented coast-line like that of North-west Europe, of Greece, 
and other parts of the Mediterranean lands, of Alaska, and 
many other regions, is the result of subsidence—the inlets 
and fiords are merely the submerged lower reaches of old 


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