The characteristics of the coast of Maine are due chiefly to the fact that a mountainous region of hard rocks, once worn to a peneplain, and after a subsequent elevation deeply dissected by north-south valleys, has subsided, the depression amounting on its southern margin to as much as six hundred feet below sea level.  Drowned valleys penetrate the land in long, narrow bays, and rugged divides project in long, narrow land arms prolonged seaward by islands representing the high portions of their extremities.  Of this exceedingly ragged shore there are said to be two thousand miles from the New Brunswick boundary as far west as Portland,—­a straight-line distance of but two hundred miles.  Since the time of its greatest depression the land is known to have risen some three hundred feet; for the bays have been shortened, and the waste with which their floors were strewn is now in part laid bare as clay plains about the bay heads and in narrow selvages about the peninsulas and islands.

The coast of Dalmatia, on the Adriatic Sea, is characterized by long land arms and chains of long and narrow islands, all parallel to the trend of the coast.  A region of parallel mountain ranges has been depressed, and the longitudinal valleys which lie between them are occupied by arms of the sea.

Chesapeake Bay is a branching bay due to the depression of an ancient coastal plain which, after having emerged from the sea, was channeled with broad, shallow valleys.  The sea has invaded the valley of the trunk stream and those of its tributaries, forming a shallow bay whose many branches are all directed toward its axis (Fig. 146).

Hudson Bay, and the North, the Baltic, and the Yellow seas are examples where the sinking of the land has brought the sea in over low plains of large extent, thus deeply indenting the continental out-line.  The rise of a few hundred feet would restore these submerged plains to the land.

The cycle of shores of depression.  In its infantile stage the outline of a shore of depression depends almost wholly on the previous relief of the land, and but little on erosion by the sea.  Sea cliffs and narrow benches appear where headlands and outlying islands have been nipped by the waves.  As yet, little shore waste has been formed.  The coast of Maine is an example of this stage.

In early youth all promontories have been strongly cliffed, and under a vigorous attack of the sea the shore of open bays may be cut back also.  Sea stacks and rocky islets, caves and coves, make the shore minutely ragged.  The irregularity of the coast, due to depression, is for a while increased by differential wave wear on harder and softer rocks.  The rock bench is still narrow.  Shore waste, though being produced in large amounts, is for the most part swept into deeper water and buried out of sight.  Examples of this stage are the east coast of Scotland and the California coast near San Francisco.