340 J, D. IVES 



erratics are applied. The coarsely crystalline nature of the rock ensures rapid 

 destruction of glacial polish and striations. Their meta-sedimentary character 

 militates against the successful apphcation of Dahfs X-ray analysis methods 

 for determination of weathering products of the surface mantle. Hence it is 

 difficult to establish the relative age of the mountain-top detritus. Thus the 

 small areas of distinctive rock type become of critical importance. These 

 include: the Kaumajet Mountains which are composed of basic lavas of 

 probable Proterozoic age; part of the southern Torngat Mountains, embrac- 

 ing the slates and quartzites of the Ramah sedimentary series; the distinctive 

 Tertiary lavas of Cape Dyer in southeastern Baffin Island and a small area of 

 sandstones and shales on northeastern Bylot Island. A factor which emphasizes 

 the importance of the first three of these areas is that the sedimentary and 

 volcanic rocks occur at elevations in excess of 1200 m immediately overlooking 

 the sea. 



THE AVAILABLE EVIDENCE IN LABRADOR 

 Evidence implying extensive glaciation at high altitudes is so far restricted 

 to the Shickshock Mountains and northern Labrador. Odell was the first to 

 conclude that ice had passed over the highest summits of the Torngat and 

 Kaumajet mountains (Odell, 1933), and the author has located several 

 glacial erratics at altitudes in excess of 1200 m and two in excess of 1500 m 

 (Ives, 1957 and 1958a). Dahl (pers. comm. 1958) maintains that these "erra- 

 tics" are probably erosion residuals and the author would agree that they 

 do not satisfy Dahl's criteria. The great contrast in degree of weathering and 

 in relative abundance of glacial evidence above and below the general 750 m 

 level has been noted by several workers (Daly, 1902; Coleman, 1921; Ives, 

 1958b; Loken, 1962a and 1962b) and has been interpreted as dependent upon 

 the relative time available for sub-aerial weathering. Daly, Coleman and 

 Loken (Loken, pers. comm. 1961) have all failed to find any indications of 

 glacial inundation at the higher levels. Thus in view of Dahl's refusal to 

 accept the validity of the Torngat "erratics," the available data from the 

 Kaumajet Mountains is of critical importance. Following Odell's work, 

 Wheeler (1958) found positive proof of total glacial submergence of these 

 1200 m coastal summits. He describes erratics of gray gneiss, amphibolite 

 and pale garnet-biotite gneiss within 100 m of the summit of Mount Brave, 

 the highest point, and these erratics lay on the local bedrock which comprises 

 a basic volcanic series (Mugford Series) (Wheeler. loc. cit.). Tomlinson has 

 since found numerous gneissic erratics on the Mugford volcanics at altitudes 

 exceeding 1000 m (Figs. 2 and 3) and states that in places they are so numerous 

 as to be used as stepping stones in walking over the contrasting dark ground 

 mass of the volcanics (TomHnson, 1958, 1962, and pers. comm. 1962). 

 In this instance, Dahfs criteria appear to be fulfilled and his plea that the 

 erratics could be weathered-out inclusions in the lavas (Dahl, pers. comm. 



