MORAINAL HARBORS 1 85 



tance northward. The greater part of the accunuihitions 

 which were formed along this outer edge of ice lie beneath 

 the level of the sea. Here and there, howe\er, the)- [)roject 

 above the water, forming islands which may be of considerable 

 elevation. Nearly the whole of that part of Long Island, New 

 York, which lies above the sea level is made up of such mo- 

 raines. The greater part of Martha's \Mneyard, Nantucket, 

 and Cape Cod are of the same nature. North of the last- 

 named cape the more advanced moraines almost everywhere 

 lie wholly beneath the surface of the sea. 



As the glacier retreated it constructed many of these 

 parallel walls of debris, separated from each other by intervals 

 of greater or less width. It occasionally happens that the sea 

 penetrates into these low grounds between the morainal walls 

 and thereb\- forms considerable bays. The sheltered waters 

 about Sag Harbor at the eastern end of Long Island, New 

 York, were formed in this manner. Harbors of this nature 

 are generally shallow, and, save for the protection afforded by 

 the scouring action of the tide, are almost certain to become 

 filled with debris washed from the cliffs of drift materials 

 which rapidly yield to the assaults of the waves and currents. 



At the time when the moraines were fornied there were 

 flowing from beneath the ice considerable rivers which cut 

 deep channels through the walls of bowlders, sand, and clay 

 which constituted the moraines. Where the sea enters these 

 channels it not infrequently forms harborage grounds of con- 

 siderable value. Thus on the southern shore of Massachusetts 

 there are a number of ports lying in these depressions which 

 were scoured out by the rivers flowing from under the ice. 

 The havens at Edgartown, Holmes' Hole, Wood's Holl, 

 Quick's Hole, Robinson's Hole, are instances of this nature. 



