- 
Parr] —S- PLAINS AND COAST-LINES. 41 
evidence likewise exists around the Caspian and Black Seas. There 
is thus proof that large portions of the great plain of the old world 
comparatively recently formed part of the sea-floor. 
Along the eastern sea-board of America lies a broad belt of low 
plains, which attain their greatest dimensions in the regions watered 
by the larger rivers. Thus they cover thousands of square miles on the 
north side of the Gulf of Mexico, and extend for hundreds of miles 
up the valley of the Mississippi. Almost the whole of the valleys of 
the Orinoco, Amazon and La Plata is occupied with vast plains. 
It is evident, from their distribution along river-valleys, and on the 
areas between the base of high grounds and the sea, that plains are 
essentially areas of deposit. ‘They are the tracts that have received 
the detritus washed down from the slopes above them, whether that 
detritus has originally accumulated on the land or below the sea. 
Their surface presents everywhere loose sandy, gravelly, or clayey 
formations, indicative of its comparatively recent subjection to the 
operation of running water. 
(2) Coast-lines.—A mere inspection of a map of the globe 
brings before the mind the striking differences which the masses of 
land present in their line of junction with the sea. As a rule, the 
southern continents possess a more uniform unindented coast-line 
than the northern. It has been estimated that the ratios between 
area and coast-line among the different continents stand approximately 
as in the following table :— 

Europe has 1 geographical mile of coast-line to 143 square miles of surface. 
Northern. ; North America i - 265 . 
Asia, including the islands 3 469 es 
Africa s A 895 ye 
Southern. <South America 3 BS — 4384 i 
Australia, - ss 332 
3) 
In estimating the relative potency of the sea and of the atmos- 
pheric agents of disintegration in the task of wearing down the land, 
it is evidently of great importance to take into account the amount of 
surface respectively exposed to their operations. Other things being 
equal, there is relatively more marine erosion in Europe than in 
North America. But we require also to consider the nature of 
the coast-line, whether flat and alluvial, or steep and rocky, or with 
some intermediate blending of these two characters. By attending 
to this point, we are soon led to observe such great differences in the 
character of coast-lines, and such an obvious relation to differences of 
geological structure on the one hand, and to diversities in the removal 
or deposit of material on the other, as to suggest that the present 
- coast-lines of the globe cannot be aboriginal, but must be referred to 
the operation of geological agents still at work. This inference is amply 
sustained by more detailed investigation. While the general distri- 
bution of land and water must undoubtedly be assigned to terres- 
trial movements affecting the whole globe, the present actual coasts 
of the land have unquestionably been produced by local causes. 
