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the same way as has been noted above for peat hummocks and 
mounds. The powerful effect of frost-heaving can be seen at 
Churchill, where angular blocks of quartzite have been raised 
a considerable distance from their original position in the bed- 
rock. Soil polygons have been found in the treeless region a 
few miles south and north of Churchill. It is probable that the 
ridges commonly marking the margins of lakes and ponds are 
caused by expansion of surface ice in winter. 
Temperature is, of course, of foremost importance in 
determining the length of the shipping season at Churchill. The 
average date at which ice goes out of Churchill harbour is about 
June 15th, and the average of open water is about five months. 
The climate of Churchill is partly determined by winter ice 
conditions in the Bay. As late as 1941, Bajkov (1941) stated 
that “Many people think that Hudson Bay and Strait are solidly 
frozen over during the winter months. This is not true, however, 
for the main body of water in this vast inland Canadian sea is 
constantly open.” According to Montgomery (1951), however, 
“If Hudson Bay remained open all winter, the warming effect 
which such a huge body of water would have on the cold polar 
air flowing across it would be clearly evident in the temper- 
atures and the amount of cloudiness of the surrounding areas. 
If, on the other hand, the Bay were frozen over, it would act as 
an extension of the cold snow-covered land and, in the long 
hours of winter darkness, would add its chilling effect to the 
Arctic winds which sweep predominantly south and southeast- 
wards over the region. Certainly all existing reports from the 
whalers and explorers who have wintered there claimed that it 
was an area of open water, but the climatic research carried out 
at McGill showed little in the weather records to support such an 
opinion and much to contradict it.” 
Following establishment of a large air base on Southampton 
Island at the northern limits of the Bay in 1942, reports of those 
who had flown over the area gradually strengthened the belief 
that the entire Bay, except for shore leads kept open by tidal 
action, was completely ice-covered. Observations and photo- 
graphs made by Montgomery (1951) during the not exceptionally 
cold winters of 1948 and 1949 showed beyond a doubt that the 
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