324 A. p. COLEMAN THE LABRADOR ICE-SHEET 



One must imagine the Labrador ice as parting into two lobes on the 

 col just west of Gaspe, where the elevation is only 751 feet on the Inter- 

 colonial Eailway, one lobe occupying the Saint Lawrence Valley and the 

 other the valley of Matapedia Eiver and the Bay of Chalenr. Beyond 

 the end of Gaspe the two lobes, augmented by local glaciers from the 

 Shiekshocks, met once more and continued as a single sheet to the margin 

 beyond the Magdalen Islands, as described above. 



The driftless area of the higher Shickshocks is about 50 miles long by 

 10 miles wide, with an area of 500 square miles; and the region which 

 escaped the Labrador sheet, though largely covered by local ice, is 150 

 miles in length by about 70 in breadth, with an area of 10,000 square 

 miles, in round numbers. 



Thickness of the Ice-shp:et 



The Shickshocks give an opportunity to estimate the thickness of the 

 ice-sheet. At the col 751 feet high, just west of the peninsula of Gaspe, 

 the ice can not have risen more than 3,000 feet above present sealevel in 

 the Saint Lawrence or it would have submerged the lower Shickshocks, 

 of which there is no evidence. Drift boulders have been found on 

 Carlton Mountain, 100 miles to the southeast, at 1,270 feet; so that the 

 ice at that point must have risen at least somewhat above that level — say, 

 to 1,500 feet. If one allows 10 feet of slope per mile to account for the 

 flow of the ice, this gives 3,500 feet for the surface at the col — a very 

 probable estimate. The thickness of the ice would be 2,500 feet, 750 feet, 

 or 1,750 feet. If one assumes the specific gravity of glacier ice to be 

 about one-third that of average rock, this would mean a load equivalent 

 to 583 feet, which corresponds exactly to Fair child's determination of the 

 highest marine level at Sayabec, a few miles to the southeast. 



It is possible also to reach an approximation of the thickness of ice in 

 a north and south section through Tabletop, the highest part of the Shick- 

 shocks. On the north side of the range no boulder-clay containing 

 Archean stones, and therefore formed by the Saint Lawrence lobe of the 

 main sheet, has been found more than half a mile inland ; and it may be 

 supposed that the local glaciers or ice-sheet which carried blocks of 

 granite and serpentine northward from the mountains met the Saint 

 Lawrence ice near the present shore. The highest undoubted evidence of 

 glacier-work on the north side of Tabletop is a moraine at the outlet of 

 Lac aux Americains, 2,300 feet above sea. The glacier which built the 

 moraine must have risen somewhat above this level. Assuming the slope 



