206 Proceedings of the Royal Irish Academy. 



TALUS-BA^"KS EESEMBUXG MOEADCES. 



Owing to the extent of sm-face exposed to frost-weathering, enormous 

 accumulations of fallen blocks occiu' on the lower slopes in Spitsbergen. Where 

 a stagnant or retreating glacier occupies the hoUow, these taluses become 

 hanked up agamst the ice, and are ultimately left as terraces, with a steep face 

 towards the valley. The old Savoyards would have called these moraines, 

 using the tenn in its original wide sense : but they owe their form merely to 

 the accident that they were prevented from encroaching, like ordinary fan- 

 taluses, on the valley. Their material is derived from the ci-ags above them, 

 and has not been moved forward or modified by the ice. Such taliis-terraees, 

 when the ice has entirely passed away, may be mistaken for moraines, and 

 may give an exaggerated idea of glacial activity in the district. Uuhke 

 lateral moraines, they may be formed on one side only of a valley, where the 

 crags happen to be more continuous. An Irish example of this kind may be 

 seen on the hillsides between Mallaranny and Aehill Sound in Co. Mayo, 

 where, in addition, ordinary moraines have melted out of the ice as it expanded 

 over the lower ground. In Spitsbergen, a huge bank of angular blocks of 

 sandstone, pro^"iding very troublesome walking, has gathered along the west 

 slope of the valley between the American Coal-mine and Mount Xordensldold, 

 south of Advent Bay. There is no doubt that the glacier referred to on 

 p. 201 contributed to the regular gi-ouping of this detritus, at a time when 

 the ice formed an obstacle along the centre of the vale. 



Ireland a>"d IifTEEGLACiAL Epochs. 



The advance or retreat of glaciers in Spitsbergen seems to depend on 

 slight fluctuations in precipitation, in a coimtry where the total snowfall is 

 not considerable. The von Post and Sefstrom glaciers, moreover, have 

 retreated, while the "SVahlenberg glacier, also descending on the Ice Fjord, has 

 simultaneously advanced. Under such cii'cumstances, though the maximum 

 of the ice-age has been passed in Spitsbergen, it would be impossible to assert 

 that the region has entered on any general interglacial epoch. Were the 

 mean annual temperatiu-e to rise, precipitation in the form of rain might aid 

 in clearing away the ice, and " interglacial " or post-glacial conditions would 

 be emphasized. On the other hand, if precipitation could be reduced by 

 external changes, leading to a reduction in the supply, but lea%'ing the 

 temperature the same as it is at present, the loss of ice by melting in summer 

 might soon outbalance its winter growth. Diy "interglacial" conditions 

 would then set in. 



In judging of the reaHtv and extent of interglacial episodes in Eiu'ope, we 



