REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1*47 



In comparatively recent times, so recent that the deposits 

 formed have suffered but little erosion, the region was covered by 

 the Labrador ice sheet. Shortly before the oncoming of the ice 

 it stood at a considerably higher level than the present. The 

 retreat of the ice left the surface mantled with glacial deposits, 

 laid down to greatest depth in the old valleys, so that the surface 

 was more even than before. During the long time that the ice 

 sheet covered the region a slow subsidence was going on, with 

 the result that the retreat of the ice found the altitude some 600 

 feet below the present, a depression of sufficient amount to per- 

 mit an arm of the sea to extend up the St Lawrence and Cham- 

 plain valleys on the disappearance of the ice barrier. The sands 

 and clays deposited there are found at present running up to the 

 400 foot line and possibly higher. They contain shells of the mol- 

 lusks which lived in the cold waters and which are of the same 

 apecies as living forms, some of which are yet found in the Gulf 

 of St Lawrence, while others are confined to colder, arctic waters. 



Besides these marine levels there are standing water levels at 

 higher elevations in the valleys opening into the Champlain val- 

 ley; and these waters must have been fresh, have preceded the 

 salt water incursion, and have been held up at those levels by an 

 ice tongue which lingered in the Champlain valley after the ice 

 had completely melted away from the adjoining highlands, be- 

 cause of its original much greater thickness there. 



Since the departure of the ice sheet the region has been slowly 

 uplifted to its present hight. The marine shore lines along the 

 lake are no longer level but rise slowly toward the north, showing 

 that they have been tilted since they were formed, and hence that 

 the uplift was greatest in that direction. The elapse^ time since 

 the ice sheet disappeared is so slight that erosion has modified the 

 surface only in slight degree. The deposits formed by the glacier 

 and in the bodies of standing water which followed are sub- 

 stantially as they were left by them. 



Dannemora formation 



Of the three classes of pre- Cambrian rocks which have been 

 mentioned, the distinctly sedimentary rocks appear nowhere 



