66 GLACIOLOGY 



The granite is traversed by small veins of a dark mineral which is probably 

 biotite or schorl. The granite showed evidence of having been very heavily 

 glaciated, showing that recently there was a great thickness of ice over its summit. 

 On the summit were numerous erratics of gabbro, dolerite, hornblendic dyke rocks, 

 sphene-granite, pinkish -grey felsites, &c. Between the Drygalski Ice Barrier and 

 Cape Irizar we encountered several formidable cracks in the sea ice, evidently caused 

 l)y the forward thrust of the Tongue. On November 28, 1908, we heard one of 

 these cracks open with the peculiar noise of ice when being riven. 



It will be seen from this sketch that Prior Island is isolated from the mainland 

 rocks on the left by a low stretch of piedmont glacier ice, which appears to be 

 confluent with the Davis Glacier. Its height as estimated is only very approximate. 

 Its strongly glaciated outlines are proof of a considerable thickness of ice having 

 at one time over-ridden it. The sketch shows that the ice at its base, to the right, 

 is now only 20 feet or so above sea-level. On the next sketch, taken 2 miles 



Prior island 



Granite partly hidden 

 under snow end ice. 



Glacier Ice- 

 Former minimum \ level of Claqerjce. 



Glacier Ice 

 overlying Cranitt 



Sea fee. 



Fig. 19 



farther south, it will be seen that the north-east end of Prior Island is somewhat 

 rugged and unsmoothed, so that evidently this was the lee side during maximum 

 glaciation. 



The nature of the main coast-line immediately to the S.S.W. of Prior Island 

 is shown on the lower sketch of Fie;. 20. 



The gneissic gi*anite on this part of the mainland was here very heavily 

 glaciated in a general north-east direction, and the exj^osed surfaces were remark- 

 ably fresh. As weathering, due to the great diurnal changes of temperature, is very 

 rapid in these regions, the exposure of these rock surfaces through deglaciation must 

 have been very recent. 



The direction of the strife pointing towards the end of the Drygalski Ice Barrier 

 Tongue is interesting. The striae on top of Cape Irizar trend towards E.S.E., 

 and were evidently formed by an ancestor of the David Glacier ; while those near 

 Prior Island trend towards the north-east, and were no doubt produced by an 

 ancestor of the Davis Glacier. It is clear that the whole of the island, of which 

 Cape Irizar is the northern end, has been formerly over-ridden by an ice sheet, the 



