DAVIS: THE HARVARD GEOGRAPHICAL MODELS. 
99 
of some size find safe harborage. .Near the land the sea is very 
shallow. Sand reefs or beaches are formed a little distance off 
shore, built of sands washed in from the sea fioor by waves chiefly 
in time of storms. The reefs bear barren sand dunes, blown up 
from the beach by on-shore winds. Between reef and mainland 
there are quiet lagoons, shallow and marshy. Here and there, the 
tides maintain a passage or inlet through the reef; villages spring 
up on the mainland near by, whence fishermen may go out in small 
boats to the shallow sea. The ways of living on the rugged old- 
land and the smooth coastal plain are almost as unlike as their 
form. 
Inquiry is naturally excited as to the manner in which the sea 
bottom was raised, or the sea waters withdrawn, to lay bare the 
coastal plain. It is well enough in teaching elementary geography 
to be frank about this, and say directly that no one really knows 
exactly how such changes are brought about. Some interesting 
theories have been suggested to account for the observed facts, but 
they are not yet proved beyond doubt, and their discussion belongs 
to geology. There is no reason to believe that volcanic action has 
any essential control of or connection with elevation ; many coastal 
plains have no volcanoes near them. But the main facts remain: 
the relative level of land and sea have changed, and part of the 
former sea fioor has been converted into a coastal plain; and this 
not long ago, as the earth reckons time, for the doabs are as yet 
but little fringed by the ravines that the side streams are gnawing 
back from the transverse consequent valleys. The shallow valleys 
of the larger extended rivers appear to have been cut down almost 
as fast as the weak strata of the plain were laid bare. 
The dimensions of oldlands and of coastal plains vary greatly in 
different parts of the world where these forms occur in the simple 
relation here described. The oldland may be of more moderate 
relief and of much more habitable quality than in the model here 
figured. Its margin may be more irregular, the salients having 
been more cliffed and the re-entrants more delta’d in the time 
before the coastal plain was born. The plain may be of small 
length and breadth, or it may stretch hundreds of miles along a 
continental margin and add a considerable measure to the conti¬ 
nental width; but if of large dimensions, it is likely to have a more 
complicated history and a greater variety of features than those 
here represented. The altitude of the inner part of the plain may 
