THICKNESS OF THE ICE-SHEET 325 



of the local glacier to be 20 feet per mile for 12 miles to the present shore, 

 the ice there would have a thickness of about 2,000 feet, and presumably 

 the Saint Lawrence lobe met it at that level, but itself sloped gently 

 upward toward the glacial center to the north. On the south side of the 

 Shickshocks there is proof, in the form of boulder-clay containing Table- 

 top granites and also serpentines, near the Federal zinc mine, that a 

 glacier crossed the summit of mountains reaching 2,000 feet or a little 

 over, and drift blocks of the same kind with some boulder-clay extend to 

 the mouth of Cascapedia Eiver, on the Bay of Chaleur. From the height 

 to which erratics have been found on Carlton Mountain, as mentioned 

 before, the elevation of the Chaleur ice-lobe at this point may be put at 

 about 1,250 feet. In the way suggested, the probable surface level of the 

 ice from the middle of the Saint Lawrence to the middle of the Bay of 

 Chaleur, a distance of 120 miles, may be inferred; and, allowing for about 

 20 miles of mountain with little or no load of ice, the average thickness 

 works out to 1,300 feet. One-third of this is 430 feet, the equivalent 

 load of average rock. Fairchild's map shows the isobase of 400 feet pass-, 

 ing close to this line of section, which accords sufficiently well with the 

 result. 



Thickness of the Ice in the Adirondacks 



No other mountains of eastern Canada were high enough to project 

 above the Labrador sheet at its maximum, but a brief visit was paid to the 

 Adirondacks in New York to study ice relations, and Mount Maclntyre 

 (5,112 feet) Avas climbed. The valleys show powerful effects of glacia- 

 tion, and erratics as well as sandy till were found in the ascent up to a 

 height of 4,300 feet, where pebbles and small boulders of quartzite and 

 granite occur, clear proof of glacier action, since Mount Maclntyre con- 

 sists of anorthosite passing into gabbro. 



Probably more extended search would disclose ice-borne materials at 

 a higher level, and in any case it is probable that the ice reached some 

 hundreds of feet above the lowest portion of the glacier charged with 

 stones. The top of the mountain consists of large and small blocks of 

 native rock, some weighing many tons, piled loosely and suggesting rela- 

 tionships due to weathering only. It seems to me very improbable that 

 a great ice-sheet could have passed over the mountain top without dis- 

 lodging these stones, and it is likely that Mount Maclntyre, Mount Marcy 

 (5,344 feet), and a few other peaks a little lower were nunataks rising a 

 few hundred feet above the ice. 



If we suppose the ice to have reached 500 feet above the highest known 



