254 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



greatly in width. Along steep coasts, such as those of Labrador and 

 British Columbia, the deposits are narrow and very discontinuous, 

 consisting of hardly more than local patches. Along gently sloping 

 coasts, such as the coast of Hudson Bay, they increase to form a belt 

 more than 150 miles wide, and in the Thelon Kiver basin, northwest 

 of Hudson Bay, the width of the belt exceeds 400 miles. The greatest 

 height of the marine features above present sea level likewise varies 

 from one part of the coast to another. This height commonly reaches 

 500 feet ; and, at a few points, it has been observed to reach as much as 

 900 feet. In contrast, in northwestern Alaska it is not certain that 

 marine deposits extend above the present level of the sea. In general 

 the height increases with increasing proximity to the Hudson Bay 

 region, which lies near the geographical center of the area covered by 

 the former ice sheet. 



In the few places where exposed sections of these deposits have been 

 examined, they are seen to rest upon the glacial drift. Hence the 

 marine sediments postdate the glaciation. The phenomenon of ma- 

 rine deposits overlying glacial drift is known also in southeastern 

 Canada and New England, and is still better known along the Baltic 

 Sea coasts of Sweden and Finland. The explanation now widely ac- 

 cepted is that the weight of an ice sheet causes the earth's crust be- 

 neath it to subside slowly. As the great glacier shrinks, the sea 

 inundates the subsided crust, which is slowly rising (though with a 

 considerable time lag) owing to reduction of the glacial load. At 

 first the sea rests against shores of glacier ice. But as the ice sheet 

 shrinks and as the crust rises, the shoreline is transferred to the 

 ground vacated by the ice and is forced to retreat little by little. Thus 

 are explained the marine cover and the successive shorelines at ever- 

 decreasing levels. Evidently, then, during an earlier phase of the 

 process of postglacial uplift, Hudson Bay was very much larger than 

 it is now. 



There are indications of various kinds that the upheaval is still in 

 progress. Prominent among these are the occurrence at several lo- 

 calities of Eskimo dwellings, built near the shoreline, and fish traps, 

 built between high and low tide, now 30 to 80 feet above sea level (cf. 

 Bell, 1884, p. 37; Washburn, 1947, pp. 69-71) . Calculations based on 

 the probable amount of depression of the crust under the ice sheet, 

 and on the uplift already accomplished, indicate that in the region 

 of Hudson Bay some additional hundreds of feet of uplift are to be 

 expected before the crustal equilibrium that prevailed before glaci- 

 ation will have been restored. From this it follows that Hudson Bay 

 will gradually become still smaller. In fact it is probable that by the 

 time the movement has ended, the Bay will have become once more a 

 broad plain drained by a master stream flowing north. There is 



