200 Proceedings of the Royal Irish Academy. 



remained as reservoirs for snow at a time when the climate was too mild to 

 allow of more widespread glaciation. Such glaciation, moreover, if it had 

 set in at a later date, would have removed their terminal moraines. " What- 

 ever," he writes, " may have been the climatal condition of this country 

 during any previous period, at the time when these small glaciers existed 

 in Kerry, the mean temperature cannot have been excessively low." He 

 thus, in effect, refers the cirque-glaciers to a late stage of what we now 

 recognize as the glacial epoch. 



Boulder-Clay. 



The origin of boulder-clay has been much discussed, since Sir James Hall 

 observed its relation to the striated rock-surfaces under it in 1812.' It has 

 been generally agreed, however, in recent years that it represents material 

 carried within the body of glaciers and pushed forward with the movement of 

 the ice. The conception of a moraine profonde, ploughed up and dragged over 

 the ground, has been considerably modified by observations in Greenland and 

 elsewhere. Glaciers in Spitsbergen show, as Garwood and Gregory pointed 

 out,^ " a gradual passage from ice charged with morainic material into sub- 

 glacial morainic material which has been saturated with water and frozen 

 hard." The lower layers of a glacier of the arctic type may consist of stones 

 and mud rather than of ice. Desiring, perhaps, to dissociate themselves 

 from those who regard glaciers as powerful agents of erosion, the authors 

 quoted seem to have gone to an opposite extreme. They attribute the intra- 

 glacial moraine to surface-materials pushed over at the end of an advancing 

 glacier, and subsequently carried forward in the mass. 



The enormous quantity of such material in the lower layers and its 

 comparative absence from the surface would be enough to show that such an 

 explanation could be applied only in special cases. A good deal of ddbris of 

 course falls into marginal crevasses from hillsides and nunataks, and becomes 

 at once taken into the lower part of the glaciers ; but it is difficult to 

 associate so limited a process with the darkening of these layers by 

 stones and mud throughout a glacier several kilometres in width. The frost- 

 broken rocks of Spitsbergen lend themselves admirably to glacial plucking. 

 In many cases the ice has gathered into itself material that was already 

 loosened on the preglacial valley-floor, In other cases one can hardly avoid 

 the conclusion that blocks are being carried away wholesale from projections 



'" On the ReYolutions of the Earth's Surface." Trans. Koy. Soc. Edinburgh, vol. vii (1815), 

 p. 182. 



-"Contributions to the Glacial Geology of Spitsbergen," Quart. Journ. Geol. Soc. London, 

 vol. liv (1898), p. 203. 



