186 Frank Carney 



State near Olean. From this point, towards the Atlantic, the ice 

 margin had a southeaster!}" course, crossing the Susquehanna 

 River a few miles south of Wilkesbarre; thence the ice trended 

 more nearly east. The Delaware River was crossed in the vicinity 

 of Easton, Pa. ; and the ice-front bore eastward from New Jerse}^ 

 just south of Staten Island. A sharp moraine extends the entire 

 length of Long Island, but the ice sheet may have reached farther 

 south. From this point eastward, the margin of the glacier can- 

 not be determined. It is certain that all of New England was 

 glaciated, and it is thought either that the ice extended into the 

 area where the Atlantic now is, or that the shallower part of the 

 ocean, bordering New England, was then land on which the ice 

 sheet terminated. 



Whether all of British America was covered b}" this same great 

 ice sheet, is not definitely known. It is supposed that Labrador 

 was entirely glaciated, and that the area from Hudson Bay west- 

 ward into the Mackenzie valley was also covered with ice. But, 

 west of this river valley, it appears that the ice belonged to the 

 high altitudes of the Rocky Mountains, that is, the Rocky Moun- 

 tains in British America were covered by a different sheet, a sheet 

 of local origin. All of the other parts discussed were covered by a 

 continuous ice sheet. 



How this ice ivas formed. We are acquainted with the ice that 

 forms on the surface of our streams and lakes, but glacier ice did 

 not originate in this way. An appreciable thickness of water may 

 be frozen in a short time. Such ice differs very much from glacier 

 ice. No one has demonstrated exactly how glacier ice is made; 

 laboratory facilities cannot be arranged to give an object lesson 

 in this. Snow may be turned into a form of ice by pressure; a 

 mass of snow, a neve field, through continuous accessions, will 

 develop sufficient pressure, by its own weight, to change the snow 

 crystals into granules. This first change produces what is called 

 granular neve. In the gathering areas of the Alpine glaciers, 

 neve fields have been studied. Further pressure through increas- 

 ing weight changes this granular neve into glacier granules, 

 small round bodies of ice. Later these granules form glacier ice. 



It is impossible to reasonably approximate the weight or the 

 volume of the ice sheet that covered so large a portion of North 

 America. It is known that high mountains in New England were 

 completely covered; that southward of the broad basins now 



