352 J.D. IVES 



covered by a minimum thickness of 300 m of ice before the ice sheet would 

 have been able to drag erratics up from lower elevations to altitudes exceeding 

 1000 m (Ives, 1957). 



Another difficulty arises in High Arctic areas where the temperature of the 

 ice mass is below the pressure melting point. Under such conditions it 

 appears that the ice caps and glaciers may be frozen to their beds; consequent- 

 ly the ice becomes a protective rather than an erosive agent. The former 

 existence of a thin ice cover in north-central Baffin Island has been deter- 

 mined by the study of rock lichens. It has been concluded that up to 70 per 

 cent of the interior upland was ice-covered as recently as 1 50 to 200 years 

 ago, whereas the present-day coverage is less than 3 per cent (Ives, 1962). 

 Once sufficient time has elapsed for rock lichen growth to reach maturity, no 

 sign of the former ice cover will remain. In this instance there is strong evidence 

 for glacierization during the Pleistocene, but the evidence for a recent, thin 

 ice-cover provides an interesting example of the problem. Thus, if the question 

 is transferred to the suggested Queen Elizabeth Island refugia, it must be 

 borne in mind that the low islands, which today have so far yielded no proof 

 of glacierization, could have been completely inundated in the distant past by 

 the type of ice referred to in northern interior Baffin Island. With the elapse of 

 1000 to 2000 years (the time required for mature development of rock lichens 

 according to Beschel, 1961) following the melting off of such an ice cover, no 

 physical evidence for its former existence need remain. Recent botanical 

 work in the northwest Queen Elizabeth Islands (Savile, 1961), although far 

 from complete, points out an unusual scarcity of both species and individual 

 plants which is hardly commensurate with the concept that some of these 

 islands provided a major plant refugium throughout the Pleistocene. 



CONCLUSIONS 



1 . Weight of evidence warrants the conclusion that large areas in northern 

 Labrador and Baffin Island remained ice-free at the maximum of the Last 

 Glaciation (Classical Wisconsin equivalent) and that the situation may have 

 been similar along the northern sectors of the eastern seaboard and also in 

 the Shickshock Mountains. This prompts the speculation that appreciable 

 areas of the continental shelf may have been dry land and thus have provided 

 ample habitats for the survival of a wide range of flora and fauna. Similarly 

 sectors of the northern Labrador coast, at or below present sea level, where 

 backed by high mountains, are Hkely to have remained ice-free. 



2. The mountain-top detritus required a considerable period of time for 

 mature development and this indicates that for a similar period areas occupied 

 by mature detritus remained ice-free or covered by only thin, stagnant ice for 

 part of that time. However, most, if not all of the high Labrador mountains 

 were completely submerged some time during the Pleistocene. 



