l8o SEA AND LAND 



shaped valleys, formed by glacial erosion, are related to 

 those wliich are produced by ordinar}- rivers. In part, the 

 cutting action accomplished by the glacier is performed by 

 streams of fluid water coursiuL: beneath the ice and movine 

 forward with the violence which the weight of the over- 

 lying frozen water gives to their flow. Unlike ordinary 

 rivers, these streams beneath the ice flow up hill and down 

 as they follow the devious outline with which the sheet of 

 frozen water rests upon the surface. Athough the carving 

 of valleys is in part accomplished by these subglacial streams, 

 the work is doubtless in good part done by the abrading 

 action of bits of stone which are contained in the slow- 

 moving ice. 



In many if not in most cases, fiords are doubtless pro- 

 duced w^here river valleys, which existed before the glacial 

 period, have been deepened and widened by the flowing 

 ice. Owintj to the fact that a orlacier in creneral cuts 

 with a measure of energy proportionate to the depth of 

 the ice above the particular point, the tendency of the ac- 

 tion is generally to wear down the bottom of the valleys 

 more rapidly than tlie intervening upland country. At the 

 same time, owing to the width of \\\v. slow-moving current, 

 the channel is widened far beyond the limits given it by 

 the river which formerly flowed in the gorge. If the ice 

 action be long continued, all distinct trace of these ancient 

 rivers may be eft'aced, but in the greater portion of southern 

 New England, where the glacial wearing was relatively small 

 in amount, these old streamways are still evident and with 

 shapes not greatly altered from their [)re-glacial form. Thus 

 the principal hords from New Jersey to Nova Scotia are 

 manifestly old river valleys which have been somewhat 



