64 History of Hingham. 



KETTLE-HOLES. 



Intimately connected with the kames are depressions in the 

 surface, sometimes of considerable depth, which have received 

 this name. Their origin, formerly a puzzle to students of glacial 

 phenomena is no longer so, as nature has been detected in the 

 very act of their formation. From observations of Dr. G. F. 

 Wright upon the glaciers of Alaska, he found tbat when a con- 

 siderable surface of a melting ice-sheet had been covered over to 

 any depth with earth material, rocks, pebbles, and sand, the ice 

 thus prevented from melting beneath remained intact, whilst all 

 more exposed over the field sunk away and finally disappeared. 

 The result of this would be to leave a great mass, sometimes of 

 large area, to settle as the glacier retreated from it, with enormous 

 weight upon the subsoil below. Here it would remain until melt- 

 ed, and it might require the heat of many summers to effect its 

 entire dissolution, protected as it would be from the sun's rays 

 by its earthy covering. As, however, the melting progressed, this 

 covering matter would necessarily slide down around its margin, 

 producing ridges and hillocks of material the forms of which 

 would be more or less modified by the running water from the 

 ice as it dissolved away. With the accumulated quantity of mat- 

 ter thus deposited, the resting-place of the ice mass would be 

 much below the surrounding surface. After knowing the results 

 of Dr. Wright's investigations, it may be confidently stated that 

 there can be no longer any reasonable doubt concerning the origin 

 of these depressions. 



THE PASSING AWAY OF THE ICE-SHEET. 



Some suggestions respecting the kame ridges, the kame hills, 

 and the kettle-holes may well be presented in remarks upon the 

 passing away of the great ice-sheet that had for ages covered the 

 land. The reality of the ice spread over the whole North, where 

 previously for millions of years a tropical climate had prevailed ; 

 its increase until it hid from the sun's rays the summits of all 

 but the highest mountain-peaks ; its onward grand movement so 

 fruitful of great results, bearing as it did upon and within it the 

 material of the present hills and valleys ; and its final melting 

 away, leaving an entirely remodelled surface, — are no longer 

 questions for discussion. Let us therefore contemplate what the 

 condition of the glacier was, particularly when passing away, first 

 briefly referring to what was probable at an earlier date. 



The question sometimes presents itself to mind why, with the 

 o:.ward movement of the ice for many thousands of years, was not 

 all the loose material of the previously decayed rocks borne to its 

 termination long before the change that led to its passing away, 

 thus preventing its spreading over the land in its retreat such 

 immense quantities of material now forming the surface in this 



