48 PROCEEDINGS OF THE ACADEMY OF [1883. 



ment of the ice. The thickness of the glacier increased nortliward, 

 the rate of increase diminishing as its source is approaclaed. This 

 latter point has not heretofore been appreciated, although observed 

 some time ago b}^ Dr. Hayes in the case of the Greenland glacier. 



Recent observations by the speaker in Pennsylvania had shown 

 the glacier to be 800 feet thick at a point five miles north of its 

 extreme southern edge, and 2000 feet thick at a point eight miles 

 from its edge, while it was only about .3100 feet thick one hundred 

 miles farther northeast, and about 5000 feet thick three hundred 

 miles back from its edge. The amount of erosion caused by it upon 

 rock surfaces was in some degree a measure of its thickness, being- 

 far greater in Canada, even upon the hard Laurentian granites of 

 that region, than in Pennsylvania, where even soft and friable 

 rocks were but slightly eroded. 



The present thickness of the glacier in central Greenland was 

 considered, and the magnitude of certain icebergs detaclied from 

 it was given. A friend of the speaker had, witiiin a few months, 

 seen a floating iceberg near the coast of Newfoundland, which 

 stood 800 feet above the water by measurement, and may have 

 been therefore nearly a mile in deptli. Dr. Hayes saw an iceberg- 

 aground in water nearly half a mile deep. 



That the great glacier flowed up steep inclines was abundantly 

 proven by recent observations of the speaker in Pennsylvania. He 

 instanced the strife covering the north flank of the Kittatinny 

 Mountain, and a boulder of limestone perched on the summit 

 which, within a distance of tliree miles, had been carried up 800 

 feet vertically. 



Referring to a paper recently published by Mr. W. J. McGee, 

 who found difficulties similar to those of Professor Heilprin in 

 the assumption of a polar ice-cap of great thickness, and who 

 imaoiued the glacier to increase by additions to its outer rim, the 

 speaker held that the single fact of the transportation by the glacier 

 of far-traveled boulders to its teiminal moraine, was a fatal objec- 

 tion to any sucli hypothesis. 



Nor did he believe that the liypothesis adopted l)y Professor 

 Dana and others, of a great elevation of land in the North, was a 

 probable one The facts now in the possession of geologists do 

 not indicate such a great and local upheaval as required by that 

 hypothesis. 



An explanation, therefore, must still be sought for the southward 

 flow of a continuous ice-sheet - a flow in some regions up-hill. The 

 action of gravity was certainly not sufficient. Even in the case 

 of the downward flow of the steeply inclined Swiss glaciers, it had 

 been shown that gravity was more than counterbalanced by friction 

 of the sides and bottom, and that these glaciers moved by reason 

 of an inherent moving power of the molecules of the ice. It was 

 probable tliat similar action occurred in the great continental 

 glacier. 



He suggested, therefore, a hypothesis which, while i)reserving 



